There are 2 methods to restore default settings.
Method 1: Using a small tool, gently press and hold the reset button until the power light turns amber, then release the button. Restoring the device to factory settings removes all previous user configurations.
Method 2: Log into the device, click on Advanced, click on Configuration, click on the Restore button next to "Restore Modem to Factory Default State". The modem will reset and reboot to factory defaults.