You will need to engage some help to achieve this. Grab two ladders and two pry bars. Place the ladders on either side of the door. You will both need to stand on the opposite sides of the door and insert both pry bars.
Push and lift with all your might. At this point, you could damage the door mechanism, but that’s the risk you need to balance with getting the door open. Once the door lifts, wedge it open with the ladders.