Yes, the rein up is a good way to lighten the forehand. It also prevents
the horse from dropping the bit and thus escaping it. As the horse "takes
hold of the bit" you can then move your hand forward as much as he will take
to help the horse extend the neck outward- the first part of stretching the
back.
Another step is to add more leg when the horse pulls down at the same time
stretching the rein foreward. Engaging the hindquarters further under the
horse will help lengthen the frame and lighten the forehand, causing the
horse to lift the head and neck to a more balanced position.
In all of this work, it is very important not to use the reins in such a way
that they will shorten the neck, as that will contract the back and compound
the problem.
Beverley