Introduce them to obscure things and get them used to them. Try just picking random objects but also include things that would be at the show. Basically a whole collection of things so that you teach them to adapt to things and they will start to trust all of the things you get them used to so when they get to the show they won’t be alarmed. I’m not sure if this is the kind of help you’re looking for but it helps for some of the horses I’ve worked with
When you there take it slow and easy too. Walk him around and let him get comfortable there. Let him see everything. If you think something may scare him, give him a good chance to check it out and face his fears. Definitely go have fun!
Desensitize him to strange things he may encounter there, take him on hacks outside the barn, take him to the show location a few days earlier if possible so he can get used to the place and remember to keep calm no matter what.