Popup error message about gmail

In the Folders Menue on the left side of the email screen there are 2 mail accounts that were added before Xfinity lost the ability to connect with Google gmail.
The result is that I now constantly get the same ERROR message popping up about this deficiency which has become extremely annoying.
I have looked for a way to delete the gmail accounts to stop the message but that doesn't appear to be an option - maill accounts can only be ADDED!
How do I stop this ERROR message???