Here's how to remove the rear bumper cover.
With the hatchback open, roll the carpet away in the corners under the lighting clusters. In each corner, you'll see a reinforcing bracket - with a stud/nut between the side flanges:
That is the upper mounting stud for the bumper frame.
Also, directly below the bracket you'll see a foam backed rectangular cap that sits flush with the trunk floor. Pop the cap and in the recess below the floor you'll see another stud fastened with a nut:
That is the lower bumper frame mounting stud. Use a 17 mm socket (doesn't even need to be deep) to release the nuts that secure these four studs - 2 on either end:
Withdraw the external mounting brackets (along with the bumper frame and bumper cover) away from the body. That's it, just release those four nuts and the rear bumper can be removed as a complete unit.