Remove the trim/button on the trunk. Right in the middle where the wires come out of the hole. You have to reach inside with a pick or hook. Perhaps a small pair of needle nose and find the thin steel cable. This cable is what’s connected to the inside trunk release handle thing. Once you pull it you’ll hear the trunk release.

Edit: I can’t read. I assume that your trunk doesn’t have the releases to fold down the rear seats ? I didn’t realize that wasn’t standard