Windows says that my password is incorrect

I changed the administrator account from the Microsoft acc to another user and restarted my PC as I was instructed. Now, I can’t sign in using the new admin account for it says “you need to be online the first time to set up your account”. So I’m signed in with a standard account now. I asked for help in Microsoft support and was asked to uninstall third-party antivirus software but I wasn’t able to do it for the action requires admin permission. Now here’s another problem. whenever I enter the admin password (which I figured is my Microsoft account password ‘cause I didn’t set any PIN) it says password incorrect.

I tried another solution which is using safe mode but can’t sign in either. says my password is incorrect again. I tried and tried, even using an on-screen keyboard but it didn’t work, too.

I couldn’t figure out what went wrong when I could perfectly sign in online with that same Microsoft account.

Please help me fix the problem. Thank you!