You have to get one of those old fashioned nail files that have the little handle then for like five minutes everyday file it down, but make sure to hold their head still so that it doesn't shake the crud out of their brains! Lol then I'd get a hair band and wrap it around their beak for like an hour and bring them inside and over time it heals itself. But if you have a super super bad case it could hurt them to put the band on.
It sounds like braces for chickens...
I wonder if those little black rubber bands for doing braids [dollar tree sells a big box for $1] would work for that?
One of my very first hens had scissor beak, but it wasn't bad enough to need intervention. She was awesome, and she loved peanuts! Char sui chicken I wish I had known that, it would have been neat to try to fix it.