To do what? You can train most horses to do a lot of 'tricks'. Mine will lift up any foot if I point at it, walk backwards on a hand signal. step up onto a box with both front feet when asked, put his head down or up on a voice command, turn his head and neck to either side (round to his hip if I ask) and other useful things. He will also retrieve a small plastic bucket!
I did this with a clicker, but I only taught him things that were useful for me, the farrier and the vet.
My horse will lift up both front legs for me - used to stretch out any pinches after girthing, something I have always been paranoid about.
He will also do a pretty clever trick to steal his friends' food in the food, mainly by picking up their buckets with his teeth and walking off - I didn't train him to do that one though!
I actually do know a couple of people there is this guy who does a lot of films and came recommended when I did some work experience working training the Harry Potter animals
There is a also a father/son combo that are french, but I can't remember their names. They were not so recommended, but might eb good (I was told they are a bit pervy