Note, this doesn't reset the admin password for the appliance, this is just the password for the representative portion of the site.
If you're able to login to the /appliance but not the /login page as admin, you can reset the admin password for that site by going to the /appliance login page and logging in. Next, go to Security > Appliance Administration and scroll to the bottom of the page. There is an option there to reset the admin account for the /login interface.
The default credentials are:
Username: admin
Password: password