On my car after a punch the plastic where the airbag of the steering wheel is got a little cut, my question is of there is a way to fix the plastic.
Is there a material that can be used tape, glue that makes it look good? Any technique to do it?
Because this piece of plastic is supposed to fracture when the airbag deploys, as @Mauro says, it is an extremely bad idea to try and repair it. Repairing it will change the piece's behavior when the airbag deploys, and could lead to greater driver injury.
Either leave it as it is, or replace it either with a new piece sourced from the dealer, or (second best) with a non-fractured and non-repaired piece from an automotive parts recycler.
It depends whether or not the cover on your airbag is removable. On the off chance that it is, you could remove it and pop it back out, and glue some kind of backing material in. If not, maybe you can squeeze it back so that the two sides of the crack are even, and then use a vinyl repair kit to smooth it over.
Finally, maybe you could sign up for some anger management classes?