To open a trunk with a screwdriver, first push the vehicle's front seats as far forward as possible and collapse them as far as possible. Lift the bottom of the back seat to find a bolt on either side. Loosen and remove both using an adjustable wrench, and then remove both the bottom and back of the seat. Pull away any insulation blocking access to the trunk before crawling inside.
Once in the trunk, use a flashlight to find the metal bar located near the trunk lock. It is horizontal in nature. Use a flat-head screwdriver to access the square box located on the bar. Turn it clockwise to open the lock and pop the trunk open. Put the insulation back in place, and securely fasten the bottom and back of the back seat with the bolts before driving the vehicle.
Newer vehicle models are outfitted with an interior trunk release. This is in compliance with the National Highway Traffic Safety Administration's Federal Motor Vehicle Safety Standards. This standard was put in place after the number of child deaths caused by accidentally becoming locked in a vehicle trunk rose. The interior trunk release is a latch that is easily identified and pulled to open the trunk from the inside. Vehicles without latches are permitted to use passive systems that detect humans in the trunk and unlock it automatically.