Do you have a FF number linked to the booking now? If not, add your AB number to the booking on ba.com? If you have an account number already linked to the booking, try changing to the AB number through the Finnair or QR websites. Or just call your BAEC service centre. If you want to collect avios, then you will probably need to show your AB card to get into the lounges unless, as noted by Golfmad, you can save a copy of your card to your smartphone.