You have to work on the whole horse and forget about concentrating only on the neck. I would start with the basics: Bending, flexion, walk-halt and halt-walk transitions. Use your reins to communicate, never to argue. Ask for softness, when he gives it to you reward by allowing him to be comfortable on the bit. Spirals in and out on both reins, serpentines. I have been known to spend up to an hour on a green horse just working on walking exercises!
When he is soft at the walk you can begin trot work. Don't worry for one second where his head is, his head position is just a symptom of what the rest of his body is doing. Establish a good rhythym, think in your head 1..2..1..2..1..2 and get him to stick to the rhythym. If he speeds up, half halt him back to your pre-chosen rhythym, if he slows down push him back up to the pace! This is the easiest concept to understand so work on this first! Down the long side of the arena, up the short side, change direction, do 20m circles, all in the same rhythym.
Second thing to work on is forward movement - this does not mean go faster! This means that you want to ensure that he is driving from behind rather than running on his forelegs so to speak. Practice your half halts and encourage him to transfer his weight to his hindquarters without losing any impulsion from the gait itself. Similar excercises as at a walk, clear straights and smooth turns. Feel him out during a 20m circle and think of the first two concepts as you go around: "Am I maintaining a rhythym? Is he driving from behind?" If the answer to these questions is yes then keep going! If the answer to either or both is no then rectify and continue!
Still not worried about where his head is or isn't at this stage.
Third thing to work on is straightness. This doesn't mean that you want a straight horse in the classical sense of the word. This means that you want his rear legs to follow his fore legs to follow his ears so to speak. That means that if you are on a straight then you want to be able to draw an imaginary line through the middle of his ears, forelegs and hindlegs and have each side fall equidistant from the line. If you are on a circle then that imaginary line is now a curve of the same proportion as the circle you are on with each ear, foreleg and hind leg falling equidistant from the line. If he drops his shoulder on a circle block it with your hip and keep in in line with the circle. If he swings his hindquarters out then block them with your calf and pop them back so that his bend is maintained and even.
There are a couple of other points on the training scale but I can guarantee you that if you can get him working in a rythym with impulsion and flexing around circles, that head will magically lower and he will soften, no gadgets required. That I can promise.
A word of warning: This will take time and patience and if you can possibly get someone on the ground to help give you some pointers then it will be a big help to you and a much more effective way to learn than purely reading alone! Ask your trainer if he/she knows about the German training scale.
Best of luck!!
All horses deserve, at least once in their lives, to be loved by a little girl.