Reply To: Free seat selection on AA, booked via BA

[NorthernLass]

Once you’ve booked your AA flight, you can go into MMB and ask to select your seat. You will then be taken to the AA website to do this.
However, I’ve only ever done this where the AA flight was a standalone booking, it’s not clear from your post whether your AA leg is part of a larger booking including some BA flights, so I can’t say that it would work exactly the same way if so.