Whats the general approach when being present for a meeting involving a union member who has been verbally harassing another union member?

i will not be the steward who will be present for this meeting happening soon but have been considering advice for the approach to this. this employee has been verbally harassing a newer hire because they want the job done their way..this person just has that personality to complain unfortunately.

but this person is a union member that wants representation for this meeting but i feel like if we provided any arguement that would let them walk away without any repurcussion then theyd just go back to harassing the other employee again.

whats the approach to situations like this? i think i know the answer already but would like some insight.