I figured it out

1)Set up AG

2)On day of migration remove databases from AG

3)Do full back up of db on current prod server.

4)Do tran log back up of db on current prod server.

5)Restore full back up to new primary replica. Leave in norecovery mode

6)Restore tran log. Recover db.

7)ALTER AVAILABILITY GROUP XXX ADD DATABASE XXX;

8)Restore full back up to new secondary replica. Leave in norecovery mode.

9)Restore tran log. Leave in norecovery mode.

10)ALTER DATABASE XXX SET HADR AVAILABILITY GROUP = XXX;