Loralie,

1- You'll need to remove the cranking mechanism from inside your RV.
2- Remove the crank handle by removing the screw.
3- Remove the screen by removing the two screws.  Sometimes the screens are a little tricky to get out.  You may need to wiggle it to get it through the tight opening.
4- Remove the two screws holding the crank mechanism onto the cross bar.  Pay attention to which way the crank mechanism is position on the cross bar so you can put it back properly.
5- This next step can be done from the inside or outside of your RV- At the top of the arm there is a plastic slide piece that fits in a channel on the vent cover.  Move the arm towards the front of the RV and the channel has an opening for that slide piece to detach from the cover.
If the contact with the wire was very hard, it's possible the channel was ripped away from your old cover.  That channel must be taken off the old vent cover and installed on the new one.   Or you'll need to buy a replacement channel if it's missing.
Next couple of steps performed from the roof top, outside of RV-
6- The next step is to remove the stop screw from the channel that the vent cover slides into.  This is at the front of the vent.   Once the screw is removed, slide out the old cover or what is left of it and slide the new vent cover in place and replace the stop the stop screw.
7- Then slide the top of the arm into the channel on the inside of the vent cover.  Note: make sure the crank mechanism is turned in the correct direction.

Back inside the RV-
8- Mount the crank mechanism to the cross bar.
9- Replace the screen and the crank handle
10- You should be good to go.
11- Sit down and partake in the beverage of choice......watch the sunset.

My guess is you may be missing the channel the crank arm rides in or the front channel on the vent.  And I've seen the crank arm disappear once or twice....  These are the pieces that usually end up disappearing when the vent is damaged by striking something or blown away in a strong wind.

Most of us have lost vent covers to strikes or blown off by wind....They also can get old and brittle from the UV rays...it's a pretty common repair item on RV's.   I carry two spare vent covers just in case.  For some reason they always seem to fail in pairs on my fifth wheel.  I don't drive with them up.  We do usually leave them up while camped for airflow, in sunny and windy California, the wind (and sun) will do a number on them over the course of a few years.