I've been trying essential oils and all natural remedies because they aren't anything changing hormones it's more just helping improve certain things. Wild orange essential oil from dottera is good for reducing depression and anxiety which can help the horse stay calm and collected instead of being anxious giving them a reason to be spooky.
Try going to the show place a day before the show if they will allow it, some places do and other don't. The day before let your horse settle in for acouple hours and then after that ride the horse in the arena, or walk them around the new area. This will help them get a sense of where they are and realize it is ok.
And then the day of the show you can try earplugs, lunge them alittle, walk them around a bit if possible.