"Give to pressure excercises" with your bitless bridle and reins!
Ask the head down with gentle pressure, as soon as they release, give! Ask for more until you can get the nose to nearly touch the ground. Also bending excercises with the bitless bridle. Help on the ground- bring the nose to shoulder, nose to shoulder.
The important thing is to use the lightest pressure you can NOW, so your horse will already "get it" when you're riding, and you won't end up in a tug of war.
Enjoy bitless riding ;)