A friend just booked a DL flight (ZRH-ATL) through ebookers.ch (something like Expedia). He now got a pre-assigned seat. He's traveling with a friend who booked separately on the same site and also got a pre-assigned seat. Of course they're not seating close to each other.
What's the best course of action to try having 2 seats together? Call Delta, call ebookers.ch, or just show up at check-in and try have the agent do it there?