How to re-add employee to People

I have an employee that had access to People. He also had set himself up with a demo account to ZohoCRM (not the comnpany CRM). So in order to add him to the company CRM, he changed his email address on the demo CRM account. That allowed us to add him to the company ZohoCRM.

However, after that, he could no longer login into People. I opened a case on this and was told to go to the user list and "re-invite" him. However, he does not appear on the "re-invite" list because he is already in ZohoPeople as account. However, he still can't login to this account.

Any ideas how to get around this problem?