I had the same problem with my horse for a couple of years, using wipe instead of fly spray and when I decided to try and fix it I was spraying her in three days.
Put the horse on a lunge line, fill your spray bottle with water and don't spray at the horse but rather, spray around the horse. Most likely the horse will pull away and go in circles on the lunge line. Keep spraying until he stops which might be several minutes then quit spraying after he stops. Try doing this a few times a day, spraying until he stops.
Next, start at the back feet and spray until he stops.
Get the idea? Be consistent. Work 15 minutes or so on this two to three times a day.
Most on the forum don't like to give treats, but when the horse stops I'd give a peppermint treat and a good pet down with lots of praise.
My mare still doesn't really like the spray bottle but she tolerates it, and that's fine with me.
For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.