Personally, when I have dealt with this situation, I am by no means experienced but not a novice, I tend to dismount & stop the horse. Allow reassurance but not praise & walk the horse to & past the 'scary' object/situation. In this the horse is still moving past the object, allowed to think but has the reassurance of you taking the lead. The horse may lack in confidence making him run away.
I deal with situations like this as my personal confidence has taken a beating & I feel safer. Said horse with me is much better & thinking more. Hope this helps xx
Circle him! Get him out Igbo the backward motion as quickly as possible and as soon as they start to move forward continue with out any pausing. Lots of people would say praise then for moving forward but I have found that if you simply continue like nothing happened you get a better result. So circle them and once movingly forward move on like nothing happened
When schooling him make sure to not always dicapline him backwards. If this is how they are schooled they will begin to think backwards.
If that doesn’t work try to tap him with a dressage whip lightly so he will move up to the spooky things
Hope this helps !! ❤️