I know this doesn't help much but the more you do the easier it gets!
Try to jump each fence on its own, watch plenty of people jump the course before you and walk it if possible.
But really the only thing that helps is to get out and get as much experiance as possible!
We had a few horses with this whilst working for a pro eventer, he just normally bandaged, and worked then horses as much as they could do in order to decrease the swelling.
Don't know huge amounts about it but this is what he did!
Hope he improves soon?!
You are both more than capable! When everything clicks you will be a force to be reckoned with!
Don't be too harsh with yourself (bad luck comes in 3's so you are due a change in fortunes!)
Where to next?