I was taught this over 50 years ago now by my dad, and have used it ever since with any horse, mine or training horse.
I run flat of hand down nose to just where noseband rests of halter, and very lightly tip nose towards chest and say "back", if horse resists I increase pressure very very slightly until I get movement.
If you have a somewhat "dumber" horse, you might have to gently rock nose towards chest one or two times, but usually horse picks it up very quickly.
This helps when you are backing horse from saddle, as well as gets horse off of front end and responsive to bit too.
After doing it maybe 3-6 times? And not over and over either, but just each time you mess with horse, you can just say back and horse will back off of voice.
And HATE the WWJJWHACK. Most ignorant thing I've ever seen.
Key to this is, as so much is, to use the VERY lightest pressure at first, only increasing if and when you need to.
Horses make me a better person.