You can take any number of trains on a travel day. Also in your country of residence.

But if I understand correctly, you are now in a night train to Offenburg, where you will change to Strasbourg? Which night train is that and where did you board it?

In any case, you can't cancel a travel day after it has started. But how many inbound/outbounds have you used now and how many should it be? And how many travel days? You can see that under My Pass.

If you would like to cancel the travel day of 24 March (and the inbound/outbound linked with it) because you'd only be using it from Offenburg to Strasbourg (I'm making a guess here), then you could contact customer service. Do remove the journeys for 24 March from My Pass and buy your ticket to Kehl Grenze or Krimmeri-Meinau (I'm not sure which one is cheaper) but you won't have a response until after you've arrived in Strasbourg, so it's a bit of a gamble.

If you only want to cancel the inbound/outbound, you'll also need customer service.

Thanks for responding so soon after my request. And for the link. I boarded on Nightjet/IC from Hamburg to Offenburg. From there to Strasbourg.  It is only the inbound/outbound that I would like to correct. I have now used 2/2. And used 2/4 travveling days. I will need the travelling day. So if I can take as many trains in my country of residence why was the inbound/outbound option preselected? I thought the the app could handle that I’m one way out of the country. In the link it says that I should not change the topic but there os no topic selected so I can either change the topic and make my request or am not able to make the request. 

Would it also apply to biy the ticket to Kehl Grenze and send it to the customer service for evidence?

Thanks a lot for your answer.

OK, so the app did it correctly: you took the night tain yesterday and therefore needed a travel day in your country of residence, so it also takes 1 inbound/outbound. If you change trains after midnight, then you need a new travel day and since this was still in Germany, you need another inbound/outbound.

Keep the separate ticket you buy (it's only a few euros) and hope for the best.