The Tablo's reset button is blue and is located on the rear of the unit.
To perform a reset of the Tablo, push and release the reset button immediately. The blue LED on the front of the Tablo will begin to flash rapidly for a few seconds indicating a reboot process has started. Once the LED has turned solid, your Tablo is connected and ready for use.
If you'd prefer to Factory reset your Tablo back to its default settings, the instructions can be found here.