Installed Microsoft Flight Simulator with wrong account

Hello.

I bought Microsoft Flight Simulator Premium Edition for Windows for my son.
The problem is that I may have installed the game while signed in to my Microsoft account, and not his, so the Premium content is only available when I am signed in. When he is signed in, he only has access to the Standard edition.

How can I fix this? I bought the game for him, not for me and he wants to play with his user, not mine.

Thank you, Yaniv.

:)