I'm not sure I follow what you're describing or having trouble with, but I'll try to help.
From the inside, our vents have a plastic frame held by 4 screws... pretty straightforward to remove.
As I recall, the screen is held in place by two recessed screws which are accessed from the inside. A long philips screwdriver is required. Of course the handle needs to be removed also.
It sounds like your gear mechanism is not functioning correctly... you should be able to find replacement parts if needed. After removing the frame & screen, you should be able to reach everything. You should not have to go up top to access the crank.
Happy Camping!
John.