The only way to reset the password for the Web manager of the device is to do a Factory Reset of your device. The factory rest will delete any configuration on the device, like any personalised name and password for the Wi-Fi bands. 

The reset Button of the device is located on the back panel, above the ethernet ports. It’s inside the little hole, and the owner will need a paperclip or anything else thin enough to fit on the hole. The button has to be pressed for 10 seconds. The lights on the front panel of the device will turn off and the device will take up to 10 minutes to boot up again.

Another way to solve this, is if the set up of the device using the Surfboard Central App. On the app, one can go to the menu sign on the top left side, and select Access Web Interface. There you will be able to see and copy the username and password generated by app for the Web Manager access.