You should be able to repair it from inside the trailer. If the gear box and arm is messed up try this to remove it. Remove knob or crank handle, remove the two screws, unlock the screen escape
latch. (Big red pull latch.) Lift the screen and the top by hand. As you raise them the lift arm will slide to a opening in the slide track and the lift arm mechnism shoud be free. Then you can buy a new matching lift arm and gear box. You will need to match up with what you currently have.
Pictures of your issue would help.