Lost or Forgotten Account Password, but backups seem to be working

Somehow, we have lost the password to an account, and we are getting,

"That e-mail address doesn't have an associated user account. Are you sure you've registered?"

from the automated system. However, our server is reporting healthy backups, but we have not recieved a summary report since March.

We are not sure how to get this account reset manually, or maybe a new account setup and the old one removed.