If you have forgotten your password (or need to set up your 2FA again), you can do so from the login page.
To do so click 'Reset password' which will allow you to input your email to receive a password reset email, as seen below.
Password reset request page
Once you receive your email, as shown below, simply follow the link to create a new password.
Password reset email
Once you have set your new password (see here for more details on this), you will also be asked to set up Google's two-factor authentication again for your account (see here for more details on how to do this).
Please Note: to avoid any confusion, you should delete the existing entry in the Google Authenticator app before setting up the new one (as otherwise you would have 2 with the same name, and only one will work).