Didn’t try app, just website (on multiple devices) & DB website. I assumed missing DB leg QDU-FRA would’ve been treated like no-showing for LH connecting flight (as I had confirmed seat on specific train with LH code). I thought booking walk-up ticket for that leg and checking in at FRA would be treated similarly as no-show (as it would be for flight). Absent info to the contrary, I changed the ticket to ensure I could make it home. In retrospect I could’ve gone to LH counters at DUS airport but by then it was after 10pm with 6am train and they were closed…