Building trust and confidence with a head shy horse takes time, patience and consistency. Treat his head and neck with great respect, never pushing, pulling or hitting him there. When you are grooming him or just hanging out, take the opportunity to gently touch, stroke or massage his neck, poll, ears and muzzle. Don’t force him to accept it, and just do a little each time.
Train him to bring his head to you by stroking his “bend button” at the girth. Facing your horse, stroke his girth. Put your weight in your leg furthest from his head so that your hip nearest his head is “open.” This creates an invitation for him to bring his head towards you without reading any threatening body language from you.
At first, do not touch his head when he brings it in. Slide your hand up from his girth to his withers and reward him with a nice wither scratch. When he leaves his head in and seems relaxed (perhaps he even sighs), bring your other hand up towards his muzzle and allow him to sniff your hand. Practice doing this with the bridle hanging from your left arm.
Next, gently place your hand on top of his nose as you turn forwards. Bring your right arm under his head and up over his nose to create a boundary that prevents him from lifting his head up or taking it to the right. Place the bridle in your right hand holding it in the middle. Still keeping the block on his head with your right hand and arm, guide the bit to his mouth with your left hand.