If my client can't remember his password or Gmail for his GMB page what are some alternatives to get us back in?
The 1st step is to try to log into the Gmail in question. If you can’t remember your password, click the Forgot password? button. This will allow you to try to enter old passwords to try and verify the account. Keep following the prompts until Google allows you to enter the account.
If you can’t remember your old passwords, but you have a recovery email set up, log into that recovery email. Now try to log back into the Gmail in question and Google will detect the link between the two and allow you to reset your password.
If the previous methods are failing, Google will eventually try to detect a mobile device tied to your account. If it finds a device Google will ping it and your device will ask if you are trying to log in.
Remember to always set up backup emails and log into your mobile device as backup methods to log into your Gmail accounts. Also, remember to write down your passwords or use a program to remember your login information.