Trying to add a user to our organization.  Received a message that he already has an account.  Followed the process of clicking save twice, and sure enough - he received the invitation to join this enterprise.  However when trying to login he's being prompted with an Authenticator code.  He has no idea what authenticator was used as it was years ago.  How can we reset this?

We're only a couple days into our trial period, need this resolved before we pay for the year.