ludespeedny
The best way is to go to the Email in question, click the Config button for Authentication, go to the Token tab, and click Delete Token. Now you can simply fill in all the new details (Client ID, etc.), click Submit, and re-auth to get a new set of tokens. From that point, if you have the latest codebase and latest build of the OAuth2 plugin you should no longer have expired tokens after 30/90 days. Just make sure when you generate the Client Secret that you set it to expire at the maximum length (2 years) so you don't have to generate and update a new secret so often.
Cheers.