How to get the nerve back?

I had a little nerves coming back from a bad wreck and all I can say is get on the bike and just spend time in the seat. Everything kinda snaps back like deja va and you will get the feel. It takes a little time but ride for fun and don't stress out. Once you hit some bigger stuff and get your flow you will feel fine.

I had a wreck once where I spun up the face of a jump and landed sideways and got rebounded off into a big tree and broke my arm. I wasn't very good at the time so when I came back I was absolutely pathetic. Forget jumping, I would get nervous if the bike even felt like it was going to leave the ground. I sold that bike and took about 2-3 years before I got another one, in that time I missed riding so bad that when I came back I was ready to start trying things.
First you have to want it, then you have to just do it. Example jumping, just start with a little hop, then practice it over and over until you are making it and are comfortable, then try things like jumping further, or scrubbing and seat bouncing. Its going to take a while.
I've had my bike for about a year now and in that time I have went from won't leave the ground to (at some tracks) " I bet I can triple that"
Good luck and if you can't find your speed don't worry about it, its not required. just enjoy riding dirt bikes

I had the same issue recently. Like Yamadogyz said, you just have to get the seat time in....at least that's what worked for me.