Hi EthanQ, welcome to the forum.
There are just a ton of threads with this basic question asked, and you'll find a lot of different opinions on how to do this and whether or not focussing on the head itself is what a rider should be doing.
The first thing is that a horse that runs around with his head in the air might be doing so because his back is hurting, due to a poor saddle fit. So, that's one thing to consider. And, might do this when you put pressure on the rein becuase the bit hurts the mouth due to poor fit or dental issues.
Not that this is necessarily your horse's case, but these are so often part of the problem with a horse that runs with his head up in the air, that it is wise to look at them first.
Do you have a trainer who can help you with these things and teach you reining? (something I'd like to learn, too!)
YOu can often get a horse to flex at the poll and tip his nose down by fiddling with the reins, and lots of folks do it, but you haven;t changed his attitude nor his balance and those are things that you will be working on as you move into reining. Too much fiddling with the reins to get the horse to put his head down can result in a horse that has his head down, tucked behind the vertical (coming so far off the bit that you loose contact and control, and his body is still leaning forward about to fall onto his forehand, kind of plowing forward and feels heavy .
The trick is to get him to flex his head in response to the bit AND to step well under himself .
It's a really big discussion, especially in the dressage world, which bears more likeness to reining than you might be aware of. Take a look at some of the other threads on her and see what you can gleen from them. Do a search on things like "headset" and "get him on the bit" and such.
Sorry I cannot make a more detailed explanation right now.