Put a halter and lead rope on your horse and take it for a work in the arena. Walk around the whole track and through the middle. Just go wherever you would when you are riding. When he gets anxious at a spot of spooks, stop and do some relaxation. Gently pull down on the lead rope and say 'head down'. When he gives even the tiniest bit let go. Keep going through whatever he does until his head is really low to the ground. This will calm and relax him. Once you get to this point praise him and move on like nothing happened. Through all this you need to be confident and not nervous yourself. If you are tense or nervous your horse is going to know it and he will feel no confidence from you.
This is how we dealt with this and other issues with my wb when I got him and am currently doing this to deal with this really scary spot there is in the arena
is working nicely on the ground so far I just need to see if its worked in the saddle lol