Hire a professional. If you're not experienced at teaching a horse how to float easily and be calm get someone who can.
Take him for a walk to look around as soon as he gets off the trailer/float. Lunge him if needed just keep his feet moving and him focused on you 😊
Practice a lot. Get him in there even when you don't plan to take him. After he realizes he won't go somewhere everytime he loads he will be a lot more willing. :)