[Surgical assistant asks for advice on if they are bound by their belief to not assist a transition surgery]
What the surgeon is doing it attacking a healthy organ, the man’s breasts, and mutilating them. There is no disease there. This is immoral and a sin.
The Catechism of the Catholic Church states: “Except when performed for strictly therapeutic medical reasons, directly intended amputations, mutilations, and sterilizations performed on innocent persons are against the moral law.” It quotes Densinger 3722 here.
So yes, I suggest that you refuse.