For Overexcited Horses
When you train use food that has longer chew time and is of lower value, something closer to their usual food, and have another source of free food available while you train. Chopped hay, hay pellets, soaked cubes all make good options depending on your horse. Feed large quantities of low value food, and work with a fairly high rate of reinforcement. This means you need to break your criteria down into small enough steps you can maintain a higher training speed.
Finally, when training always maintain clean food delivery practices- click when they do the correct behavior, then grab the food, keep your hand closed until you stretch your arm well away from your body to feed away from you, into their space. Train a few safe behaviors, particularly a safe default behavior for them to return to when they don't know what else to do. Standing Facing Forward works well for this (like a dog's sit/stay). As well as head down and back up or touching a target. So they have a safe and appropriate behavior to go to if they are confused or frustrated.