Is this question anything to do with "Bid Now Upgrade Success Stories"?

You can attach a QF freq flyer number to an AA reservation.
If you have a AA ffn in the AA reservation try phoning AA and ask them to change to a QF ffn
or AY manage my booking https://www.finnair.com/au/gb/customer-care#
or RJ manage my booking https://rj.com/

Would expect changing ffn after a flight would be hard to impossible.
Have read on FT of people successfully changing ffn after a flight with different airlines. But more that have failed.

Edit
AA thread :--->Change FFN / frequent flyer number on AA booking? (master thread)