Aha! Thanks. I hadn't logged in. In fact, I haven't joined yet. LOL
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This would be my first ever flight on DL: They now have the only service (via codeshare with AM) from MID, where I live, to the USA. (UA & AA normally fly here, but Covid, you know...)

If I book on delta.com, how hard would it be to switch the FFP to AM's Club Premier? Or should I just worry about that later, and do it at the check-in counter with AM?