I come out to the Trailblazer unlock it twice, pull the handle to the life gate or hatch and it just does not open. I try unlocking it again from the inside switches, same thing. Well now, what do you do with that? There is no manual lock for the rear, or at least one that is visible and the only handle is on the back. Then I come to realize it is not just the hatch that is stuck it is the glass as well.
In the owners manual it states there is a little service plug on the interior panel of the lift gate, from there is a set of levers to manually unlock the lock. Using a screw driver, lift the lever on the left upward, it should click and stay there. Then take the lever on the right and push it to the right, it should click. After that you should then be able open the lift gate from the out side of the vehicle.
Note the Trailblazer SS has air bags in the rear, and after sitting a few days can become uneven seemly jarring the lift gate. Before I could get mine to unlock I had to let the bags fill up all the way and then do the manual unlock, otherwise the lever on the left would not go all the way up. Once it is opened up I would suggest cleaning and greasing the lock if it needs it!
As long as the rear electronics and servo are working this should resolve the issue and return to functioning properly!