There is no "manual release from the inside". However from the inside you can remove the trunk trim panel to gain access to the latch stricker. It is the "U" shaped anchor that the latch closes/locks onto the vehicle. There are two bolts that hold the stricker in place. IF you can remove those bolts the liftgate will then open. YOU should check the anti theft system for any DTCs (Diagnostic Trouble Codes) as your very first step, and be sure it is not a broken air line or vacuum leak. If it is a broken air/vacuum line the lock will remain in the position it was last before the rupture, and you usually can hear the air escaping when you activate the lock or unlock sequence.

Hopefully someone with first hand experience can give you better advice.