Through the Deutsche Bahn app, I booked a trip for two from Munich to Locarno. The first leg is Munich to Zürich for which I booked seats. For the second leg, a non-stop IR train from Zürich to Locarno, there was no option to book seats through DB. I went to SBB.ch and could see no way to book seat reservations. I feel like I must be missing something obvious but I can’t see where to do it. Any help or advice will be appreciated.