After watching hundreds of videos and seeing riders struggle with this, I though a short article with a quick drawing might be of help if you are struggling to know exactly what is needed.
What is the judge looking for? A complete release of the reins (or rein if only one rein is required to be released). You should have loops! In other words, a clear release of contact, not just a loose rein.
Hopefully you will find this of help:
Preparation: At least four or five strides away, check to see if your horse is as balanced as possible, has the right bend if you are turning on a circle and you are aware of the rhythm under you. A few little half halts may be necessary.
Few steps prior: A couple of tiny releases with your hand. Make sure they are tiny enough the judge will not see them, but clear enough for your horse to pay attention and prepare for you to completely release the contact.
During: Gently move your hands forward (without you tipping forward yourself, otherwise you will find your horse will fall onto it's forehand with your weight). They must go FORWARD towards the horse's mouth, NOT up in the air.
There must be clear LOOPS in your reins!
After a stride or two, and you have a clear release of the contact, bring your hands back smoothly and gently so don't cause your horse to throw it's head up.
The judge does not want anything to change. When you release the rein, the horse should not fall on the forehand, raise it's head, come behind the vertical, lose balance, rhythm, impulsion or alter the tempo. The 'frame' should stay the same. Obviously this is what we are aiming for however, it may take a fair bit of schooling for you and the horse to perform this movement really well, but you will find your marks increase the more you both practise this.