Outlook 2016 problem

The customer has had Outlook 2016 on his PC for a few years but has not been using it because someone somehow set up an email account that he does not know the password for.   It was an insurance agent that came in one day and set up an email account that ties to the agent's company Exchange account--strange as that seems.

So today I helped him add an IMAP account that works fine, and made it the default, hoping I could then delete the bad account.  But I get this error:

"You cannot delete this Outlook data file.  Configuration information in the file is being copied to your new default data file.  You can delete the file after this information is copied."

Somehow I doubt that will ever happen, as this has been going on for hours now.  If I uninstall and reinstall Outlook will that solve the problem?  Is there an easier way to delete the bad account?