You just remove the wrong jouney (train) from your app and then add the correct journey (train). But you should not activate your pass and travel days until just before boarding the first train of your travel. Please read more about that in my next reply. 

Here is some useful information from the experienced travellers in the Community regarding both planning, reservations and activation of pass and travel days. 

 Planning

The rail planner is normally not up to date, as it only is updated once a month, so to be sure of the time table you better check the timetable and availability on the websites of the national railways. The bigger national railways, like DB (Germany) SBB (Switzerland) and ÖBB (Austria) cover several countries. 

 Reservations 

Thanks for responding and I’m grateful for the advice. I shall remove the train wrong journey and replace it with the correct one. Now however I am rather confused about the difference between activation of the Pass and activation of the Travel Day(s), and how they both work. The advice offered is as follows:

 “Activation of pass

During the activation process you choose the start day of the validity of the pass. Once the validity has started it can't be changed even if you haven't travelled. The advice is therefore to wait with activating the pass and starting the validity until the first day of your travel as you only can deactivate the pass no later than 23.59 CET on the day before the validity starts. If your travel plans change in the last moment you can't deactivate the pass and change the validity. 

It can be wise to make a test and activate the pass with a start date well in the future and then deactivate the pass immediately, just to see that everything works.

 Activation of travel day

The advice from the experienced travellers in the community is also never to activate a travel day, that is connect a journey to your pass and create the ticket (QR code), until just before boarding the train, otherwise you might loose a travel day if your travel plans change in a late stage  You can't delete a travel day in the past. A travel day can only be deleted until 23.59 CET the day before the travel day.”

From looking at the screen grabs below is it possible to tell whether my Pass is activated? I guess it must be because there is the option to deactivate it, but why would I deactivate it and how can one plan a trip without activating the Pass?

Also, from looking at the screen grabs below, is it possible to tell whether my Travel Day (4/04/2023 - London-Paris Nord) is activated? If not, then how do I activate it - and all the subsequent travel days, none of which I have decided upon yet?

And finally, looking at the screen grabs below of my Pass, is this all I need (apart from reservations on certain trains) to travel around Europe for a month, or do I need to upload tickets (QR codes) for each leg of my journey?

Apologies for the length of this query and for my level of ignorance in these matters. 77 years of age and very much a newbie to all this. I will improve with practice and good advice.

Best remove your personal details.

But your pass is activated. Otherwise you cannot use the little ledgers grey/yellow ledgers next to the journeys, under your tab “My Trip”

When a little ledger is yellow, you also have activated a travel day. Just tap on it again, and you’ve deactivated the travel day :)

I’m going to recycle an reply I made a couple weeks ago, that’s similar to your questions, based on a trip I did in summer:

Circled in green are the trains I added in “my trip”. You can tap on the grey ledger to transfer it to your pass. I actually only took a train later that originally planned, so I didn’t need to activate the first journey.

Circled in red are the trains that I effectively used, and that got transferred to the pass.
These generated a qr-code. Note the yellow ledger.

Further tutorials and user guide about using the pass can be found in the link below (with a little video clip:)

https://www.eurail.com/en/eurail-passes/eurail-mobile-pass/getting-started

You can't cancel activation of a travel day this way. That can only be done via My Pass: select a travel day and then Cancel travel day.

Ah voilà, thanks for the clarification. I never activate travel days in advance, so I never had to do it

Thanks to both for your kind advice. I did look for a means of scrubbing my personal details, but could not find a tool to do so.

Question for rvdborgt:

“You can't cancel activation of a travel day this way. That can only be done via My Pass: select a travel day and then Cancel travel day.”

I hope you will forgive me if I’m mistaken, but when I go to My Pass there are only two options - Show Ticket and Deactivate Pass, whereas under My Trip the three dots menu (top right corner) allow an option to Delete Journey. Would that be the way to deactivate a travel day? I am looking to cancel a journey I erroneously activated for the 1st May when in fact I intend to travel on the 2nd May (for which I have a reservation).

"Delete journey” does just that: delete a journey from your trip. It does not cancel a travel day.

If you have a continuous pass, then the only thing you can do is to deactivate your pass. After that, you can activate again, selecting another start date if needed. It's wise to do this only on your intended start date.

If you have a flexipass (X days in 1 or 2 months), then you can cancel individual travel days in the way I described, and after cancelling the last travel day, deactivate the pass.

Okay rvdborgt, thank you very much for clearing that up for me. I get the difference now. In fact I do have a continuous Pass, and so, for the sake of complete clarity, since I am looking to reschedule my inbound homeward journey from Antwerp to Newcastle (UK) from 1st May to 2nd May is it the case that I should delete from My Trip my mistakenly planned journey of 1st May (Antwerp-Newcastle) and then simply use the Planner to plan it again, but on 2nd May? I realise that this is probably the case, and that I could be testing your patience here, but that’s a risk I’m prepared to take for my peace of mind.  

Correct :)

And if I were you, I'd also deactivate the pass until the day I start my trip.

Thanks for confirming. Appreciated.

Would you be good enough to advise me why you recommend deactivating the pass until the day I start my trip?

Making predictions is difficult, especially about the future.

You never know what will happen. You can only cancel activation of the pass and also of any travel day until 23:59 CET before validity starts. If something unexpected happens after that, you wake up ill or whatever, then it will be too late to cancel activation and you'll lose travel days.

Nicely explained. Got it now. Grateful thanks rvdborgt.

(“Making predictions is difficult, especially about the future”.)

 As opposed to predictions about the past and present? 

Just teasing.