Gently raise liftgate is right, ! I would not loosen the tailgate hinges tho.
Having another set of hands, even use slight prying pressure in the gap while closed? And then raise.
I have the same issue, began when I replaced the liftgate with a replacement, less rusted/repaired/repainted. Then the rear wiper only worked intermittently, due to the ground path being incomplete (through the latch at sides). Now I have less hair than before. :lol:
Perhaps loosening the top...