I bought a train ticket from Stuttgart to Munich on the DB Bahn website. My wife and I are supposed to be in first class (it was like 10E more). They emailed me an "online ticket" but there are no seats on it. It just says to bring my American Express with me. How do I know where to sit? Will they assign us seats before we travel? Do we have to exchange the "online ticket" for a real ticket at the station? I'm just confused. Thanks in advance!