The top horizontal trim (behind the high level brake light) needs to be pulled out first as it overlaps the 2 upper side trims.
Then the side trims come off, followed by the largest lower main trim.
As Ian says, all trims are held in place by clips, so you may want to ensure the parts aren't too cold and brittle before attempting to tug on them. Get them up to at least room temperature. Try to pull on the trims as squarely as practically possible to minimize the risk of lug breakage. The rear lights access cutouts (in the lower main trim) can be used as leverage points to your advantage.
I have the facelift, and access to the switch is limited as it's secured to the bottom of the exterior chromed horizontal trim that's held in place by 4 nuts - and the access to these 4 nuts is fiddly, well at least in my car.
So rather than going that route, I suggest inspecting the wiring exposed by the trim removal first. This would be a good time to pull back on the rubber loom gaiters to inspect wiring at their 'flex' points, as suggested by Gregers.
If all is well - would I then attempt to gain access to the switch itself.
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