You must remove the glove box first. Three metric screws (7 mm head) on the hinge located at bottom side of glove box door. Then remove connector from back of switch. There is a small tab at very back bottom side of switch that must be pulled downward slightly to release the connector and you pull connector toward front of truck. Then there are two very small ears (tabs) holding the switch into the lower dash. The ears are located on the upper and lower sides of the switch and the upper one can be clearly seen in the second picture attached below. Both ears must be depressed into the switch body to release it and the switch will come outward from front of lower dash (toward rear of truck).
The switch is a membrane type of switch like the key fobs and center console switches and subject to the same dirty contact issues. The part number of the switch is 10369711 and is unique to the SSR, but unfortunately is NLA. Good news is that there is a compatible switch (just has car with trunk on button) used in I think it is the Malibu platform. Contact Mike Byers in parts via PM (site name Byers) or calling directly to Classic Chevrolet Parts in Grapevine TX, and he will get the switch you need. I wouldn't mind getting your old switch to play with once you get a new one installed.