I just booked my first Avios award travel for later this year. ATL-MIA-BGI-MIA-ATL. A few questions. I have an AA credit card that would waive baggage fee. Do I just show the agent my card when checking bags? How can I go about changing seat assignments? Is this done thru BA or AA? The only option I see is to view seats thru BA website but not able to change them. I have no elite status in OW.