ok this is how the lock should look empty. You just slide the hoop onto that bracket there. There is an open end in the bracket so it will just slide in. Unhook on end of the lock thing and loop it threw the helmet and then back threw the bracket like this
I found 2 ways to place the helmet, one over the side of the bike and one just sitting on the seat I'll show both.
Pushing the rear seat back on can be a little tricky at first but once you do it a few times it will get easier.
Hope this helps and I hope this works, I'm posting from my iPhone.