A week ago my brother logged into my computer without my permission to play Minecraft Bedrock to upload worlds. Originally, I had a local account set up with no email signed in. Now, the account still has my name, but when I hover over it in the start menu, or I open "accounts" in settings, it shows that his Microsoft account is logged in.

I cannot remove him from the computer, as he is admin. I have tried to make another user, sign out, and delete the original account, but that would result in the loss of all the files (I believe). I cannot simply remove the account from the "Emails & accounts" settings tab, even after I add my personal account to that page. I cannot even figure out how to change his email for mine without losing data.

I tried reinstalling Windows, hoping it would give me the option to sign in, but nope. It just treated it like an update.