My advice would be to take him for a walk in hand. My wb started freaking out at a certain point in the arena and I was struggling to deal with it from the saddle (im not a big person and he's huge and simply over powers me sometimes.)
I decided one afternoon to take him for a walk around the arena while doing this to directly keep his attention on me not the monster hiding in the trees that is going to jump out and eat him
the first couple of times he lifted his head to look and I instantly changed directions away from the scary place. Then I would run with him for a while and stop and try to go past again. After a little while he just had his head down as he walked past the spot and hasnt had an issue with it since.
Make sure that whatever you do you are 100% confident in what you do or he will sense that and instinctively feed off your fear.
Approach and retreat is another method. Walk your horse to the spot where he will go no further but don't push that threshold. When he stops turn around and walk away a little. Turn around and go again. Each time you want to be getting a little bit further than the last time. Never push him past his threshold though as that can make things a whole lot worse.