If GoGuardian or another school management policy has blocked Microsoft Store, there isn't a legitimate way for a student account to override that restriction. The block is controlled by the school's admin/IT, not by the Microsoft. It is not anyone else's place to override that.
If you need an app for school, the appropriate options are to ask the school IT/admin to allow the app, install it for you, or make it available through whatever managed app portal the school uses.