Are you saying that you cannot access the account in Thunderbird? If so, I suggest you go to privacy&security, click savedpasswords and then showpasswords and the highlight and delete the two rows for the account. That will remove the password such that you should get the Google prompt again.

HI David, I tried that, but it says Sending of password for user [email protected] did not succeed. Mail server pop.gmail.com responded: [AUTH] Application-specific password required: https://support.google.com/accounts/answer/185833

Do I have to reset to normal password and then go back to 0auth2?

You will need to delete the password/s that start with oAUth:// and uses your email address as the user name. This is the actual token being used, not your password.

Login to server pop.gmail.com with username [email protected] failed. Enter new password. It wants a password, but it doesn't accept the one setup in Gmail. It wants a 0auth2 token but I don't know how to regenerate that.

Please recheck my earlier post to verify that there is no password stored in Thunderbird.

Solved through extensive googling

Solved through extensive googling

And the solution was? Knowing what the solution was will help us in the future.

ONLY if you have 2 step verification enabled, Go to your google account and select Security. Under "Signing in to Google," select 2 Step Verification. At the bottom of the page, select App passwords. Select Generate. The app password is the 16-character code that is generated. To enter the app password, delete current logins for that account in Thunderbird, then try to access it and when prompted for a password, enter the 16 character code and tick for password manager to remember it. Done.