Reservations are not connected to the app.
App is the ticket, you should add the train and activate before travelling and show the ticket/barcode generated. Keep the reservation, either printed or on phone as PDF and show this if requested.
Have you looked at the film about setting up the mobile pass?
https://www.interrail.eu/en/interrail-passes/interrail-mobile-pass/getting-started
Then, read the advice from the experienced travellers regarding activation of pass and travel days below. I suggest you deactivate your pass today in case something unexpected happens before your planned departure tomorrow.
Here is some useful information from the experienced travellers in the Community regarding activation of pass and travel days.
Activation of pass
During the activation process, when you choose the start day of the validity of the pass, the first day of the validity period is automatically made a travel day, even if you don't enter a journey, the advice is therefore not to activate the pass before the first travel day as you only can deactivate the pass before 00.00 on the day the validity starts. If your travel plans change in the last moment you will loose travel days if you have activated the pass in advance.
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, 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.
