If you hold a Platinum or Aspire card, -and- have not yet used any of the 2021 credit, customer service will almost certainly change the airline selection if you ask politely by telephone.
I just changed mine today via the Chat box on the desktop site - took all of 2 mins and they have that reason pre-loaded in the automated chat assistant if you type in "Change Airline Fee Credit Selection" or something similar. It will ask you if you've used any of the credits, what airline you want to switch to, then they have a person ping you the disclaimer and confirm the change. Got the email confirmation a couple seconds afterwards.