Is there a tab which invites you to go to AA.com to select seats? It should then take you to a screen which displays the AA PNR.
If this is more flights in a complex itinerary (so the second AA flight after a BA flight and after the initial AA flight) you may need to ring up for that.
Edit: Actually I've checked one of my bookings: the screen is not showing all the usual details, which is an occasional bug. It should come back within a few hours / days I guess.