gearbox stuck on 2003 GMC Envoy

I tried to put my truck in gear but the button on the side is stuck. therefore I can not put the truck in drive or reverse. how do I unstick this button.

Asked by for the 2003 GMC Envoy
The most common cause for sticking shifter parts is coffee or soda spilled into the shifter. The shifter can be removed and cleaned under hot water if necessary to remove any spill residue.
1 more answer
I had the same problem, when the tow truck showed up he raised the envoy and looked, the linkage has a bearing and when worn the linkage seperated from the shifter rod, we sliped it back into place and used a tie wrap to be able to shift into drive. Tomorrow I will go to the dealer and by the linkage that has the bearing and have it relaced. I feel this part could of been made with a much better long lasting linkage. ( if you would look at the linkage you would agree with me.