To unlink your Google login and change it to an email & password login instead, go to your account settings from the dropdown menu in your profile icon. You can also follow this link:
In the account section you'll find the Login method:
Click the red 'Unlink Google account' button. You will be prompted to enter your new login credentials:
You'll see a confirmation message and then you'll have access to the 'Change Email' & 'Reset Password' account settings:
💡Tip
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.
⚠️ Note
If you're still having trouble, try using another web browser. And make sure to log out of your Google account first.