With authenticator app, the device must be registered. The point of MFA is it takes a password and some other information, text, email or device.
you can login to your account on the web (you will need to have registered an alternative authentication method if using MFA, say text or alternative email ). Once loggedin you go to security and add an authentication method. Pick authenticator, the other, then a qr code will appear. You scan this with the app.
if you don’t have an alternative method, you will to contact the account admin and reset the account.