There is a physical reset button on the underside of most routers. Holding this button in for 5 seconds, after the unit has been powered on, will perform a factory reset on the router. When the reset is initiated in this manner, the LEDs on the front of the router will flash to indicate a reset is in progress. The router will automatically reboot once the procedure is complete.
Do not remove the power while the router is running this reset procedure. Using this method will not preserve any settings.
Locations of reset button, for various model TransPorts:
WR11 - if looking at the side of the unit, where you can see the Service, Signal, and Power LEDs on the top-left, the reset button (hole) is to the far right.
WR21 - if looking at the front panel of the unit, the reset button (hole) is just to the left of the USB port.
NOTE: The WR44 RR model does not have a physical reset button. (Need to use Digi FlashWriter utility to reset unit back to factory settings)