First, remove the access panel on the inside of the tailgate. If you can get 12v power to the connector wires to the window motor, it should roll down if the motor is still working. If it's not, you can unbolt the glass channel at the bottom where it attaches to the regulator (4 bolts). Put some zipties or tie the two regulator arms in the up position before doing this, or they will snap down with great force when you take off the glass. Check the wiring to see if it's broken anywhere inside the tailgate. You can also try pushing on the tg from outside while trying the keyswitch or someone tries the dash switch. There is a safety feature that will not let the glass down if the tg is not closed properly. Worn or misaligned striker bolts are the cause of this, or a bad switch. Just be careful not to break the glass, and watch those fingers!!!!!!!!!!!!