I can't access my Microsoft 365 Business Premium account

A Microsoft Business premium subscription is a commercial subscription. To access the subscription details you'll need to login with the admin account you created when you first established that tenant. You can reset the password for that if need be. A commercial tenant like M365 Business Premium doesn't support a personal email account as an admin. you need the one that was created when you set up the environment.

Failing that contact the MS support details that should be in the email your received or look them up on the web for assistance I suggest.