It's dead easy to get to - mine started playing up whilst I was replacing my upper tailgate.
Three 'captive' slot head screws - turn 90 degrees and the carpeted liner simply pulls out, (the far end simply slots into a recess).
The button is hel by two Philips screws and you then twist the switch 90 degrees and it pills out of its recess.
Unplug it's connector and there you have it.
The switch, itself, can be stripped further by pressing a small lever, (at the base of the switch - near to the contacts), and twisting the locking ring and the switch will drop out from the button assembly.
I simply sanded the button base, (it was catching), and I now have a fully functional smooth tailgate button!