If you have rear speakers, remove the speaker cover, remove the speaker(s) and reach in and find the mechanism and turn to open. I did this with my 1996 Lumina Van.
I just went thru this on a 2002 s-blazer. On the rear tail gate their is a punch-out in the rear inner gate panel. It is in the center on the gate at the top of the carpet. If you peal the top center of the carpet down carefully their is a small punch-out behind the carpet. The punch out is about 3/8 of a inch tall and about a inch long. If you punch this out you will see a gold colored lever in there and you can take a screwdriver and stick it in the access hole and slide it to the passengers side of the vehicle, this should pop the rear glass open. Good luck.