If I book an AAdvantage Business Saver FF Award tic for AA flight connecting to Air Berlin Flight in MIA to Berlin and itinerary shows seats unassigned for AB portion - how do I proceed to to have those seats assigned? My concern is that although the business seats are available when I book award tic the seat assignments might not happen in a timely way and then I would be flying coach.

Can this happen? Is it better to actually speak to an agent and have them book and assign?