I've got a scissor beak hen of 7 years old.
From time to time her beak grows so long that it locks on itself.
If that's about to happen, I pick her up from the roost bar in the evening, wrap her in a towel and very carefully clip her beak with nailclippers for dogs.
Since her beak is gray, it's a bit difficult to see the living nerve, there has to be very good lighting when clipping.
She doesn't like the clipping at all, but sits bravely more or less still. With the towel, it can be done by one person only, the towel holding the hen in place, one hand around her head, the other clipping. But its better with two people, one holding the hen, the other can concentrate on the clipping.
As an emergency backup I've got a powder that stops bleeding at hand, made of green clay powder with ground yarrow leaf powder in it.
Since her scissor beak is quite pronounced, it's difficult for her to eat grains or pellets (but she's mastered the art of clipping grass).
That's why there's permanently a mug in the feeding tub. Whenever I add grains/pellets, I pour them into the mug, so that the mug overflows into the tub.
It's easy for Scissor beak to eat from the mug - she doesn't have to pick up the grains with her beak but can just dive in with an open beak