You are not trying to promote the pawn, you are trying to use the pawn as a decoy so that your king can take all the kingside pawns. I would create the queenside passed pawn and then rush to the kingside as quickly as possible. Their king will not be able to defend the kingside pawns because it has to make sure that the queenside pawn will not promote. While the king is dealing with that, you can feast on the kingside pawns and easily promote one of your own kingside pawns
This is the idea, you lost the a-pawn but you are able to pick up the black kingside pawns while the black king is on the a-file.
Hope this helps!
Any constructive input will be highly appreciated. Thank you!