How to free up fresh air vent door?

Thanks for the replies everyone. I was able to get the latch freed up by tapping on the handle with a hammer and working WD-40 into it. I ended up grinding of the hinge-to-box rivets with a dremel and once I had it off the box I was able to get the hinge freed up as well. I think I’ll still buy me some evaporust and soak the door and hinge assembly before I rivet it back on the box.