get him a good light and walk with him and show him there are nothing to be afraid of.it will take time and lots of walks in the woods to help.
The only thing is time.explain things as they are.make sure you don't scare him in any way.that would drive the last nail in him coffin.just be a friend and let him talk about it to you.show him we all get scard of something at some time.
hope you can help him.being scared is a terrible thing,it took me a long time to go into the woods by myslef.
start a first light and just at dark and work from there.start a few min earlier and later each time.