There is an option to unlink your Google login and change it to an email & password login instead. You can find it in your account settings:
Go to your account settings.
Click Unlink Google login and use email instead.
Sign in with Google using your current account.
After signing in, you might get stuck on a blank screen like this, you can close it.
4. Go back to miniExtensions website and enter the new email. (if after you select your account in the Google pop-up, you don't see this screen, try another browser)
If you're having trouble unlinking your Google account, you can just "reset your password". Go to the login page and click "forgot my password".
You will get an email to set a password. Your Google account will then be unlinked automatically. Log in again (without Google) and change your email address.
If you're still having trouble, try using another web browser. And make sure to log out from your Google account first.