If you connected your gmail/gsuite account to your email and you have changed the email in your account, you will need to reconnect it to the new account . Go to your custom email sending server set up page and click Disconnect to remove the current connection and then you can connect with the new email you have added to your account.
As an alternate way to do this:
Use this link: http://phoneburner.com//google/do_logout ( log in and copy and paste this into your browser after) to disconnect your account from the current email you are connected too.
This will log you out of Phoneburner and take you back to the log in page.