There should be an emergency trunk(rear) cable behind the rear wheel liner on the driver side. You should not have to remove the rear bumper. According to others remove your wheel, remove the liner, and dig for that cable and give it a yank. Here's an image from renntech. I have not done this as of yet; only experience with the frunk cable. It's possible the previous owner re-route the rear cable.
https://www.renntech.org/uploads/post-4-1164692198_thumb.jpg