If an employee have left your company, the administrator for your account should delete the user account and create a brand new one if anyone else need access to Avinode instead. You should never rename an existing account (unless spelled incorrectly).
Renaming an account will cause problems going forward ie. you will not be able to change the security email and thereby ask for a new password.
Avinode cannot in any way access the credentials on user accounts, only the user themselves have access to them.