You can send an email providing instructions to the user on how to reset their password on the Staff Users tab (Setup > Staff and Users Access > Staff Setup)

Click the ellipsis  in the Actions column and select Send Reset Email.

NOTE: If multiple staff members use the same e-mail address, each will receive the reset password email. Within the email a link in the email to each associated account is provided. For Example: If Betty and Sue both use the email address [email protected] but each have their own login name to the tenant. Betty asks for a password reset email and when it arrives she knows which reset link to select because it is identified with the login name that she is used to using.