If you can't remember the password to enter your modem's interface, first try the default username and password "admin" in both fields. If it's not that, then try a factory reset to reset the password back to the default password.

Please note: A factory reset will reset all modem settings back to default, including your WiFi password/name. This means if you're on the WiFi when this procedure is performed it will disconnect you and you will need to reconnect manually if the network name or password has changed as a result of the reset.