To reset the Surface Unit Wi-Fi password to the default 1234567890, simply push the reset button under the blue rubber lid, between the two antennas, for 1 second. To make a full factory reset push and hold the reset button for 15s while the device is powered on. Once the button is released the LEDs will blink back and forth while the unit is resetting. The Surface Unit will then reboot automatically with the SSID and password as marked on the back of the Surface Unit.
Read more: Surface Unit Settings (Wi-Fi)