Having the DB Navigator app and your tickets loaded in is the most practical thing you can do to make your travel life easier on Deutsche Bahn. When the train works it is incredibly convenient and fluid. When it does not, which is more often that they should it can be more difficult but the app helps a lot.
Learn to use it before as it is quirky and "german": it works but you need to know how to do it. The message are notoriously customer unfriendly.
Beware of this particular situation: if the actual metal that was scheduled to do your service has a technical issue and there is a swap to another physical train, they mark it as cancelled in the app. The service with the equipment change will have a different number but exactly the same schedule, your ticket is valid on it. But as the number is different it shows as cancelled on the app. All "logical" but very unfriendly.