Make sure you are breathing and relaxed. You can talk the horse or sing your abc's. Also when the horse jigs tell them that's not allowed by doing a more forceful half hault. You can also make the horse back when they jig to teach them it's not going to get them there any faster.
he's hot. you need to sit back & relax. do things to keep his mind on you & make him think. don't lay on his mouth but keep a soft contact. sometimes raising your hands up a bit will help stop them from jigging.
I worked with a pony who jigged awhile back, the best way to deal with it without disrupting her ongoing training was to ask her to halt whenever she jigged and back up a few steps. This made it clear that when moving forward, her only options were w/t/c. It also helped to reward her if the walked nicely, a "good girl" can go a long way.