Enter variable to rotation during animation

so I have this
my sword object has the variable angle which I want to add into the z rotation during animation.
The problem is I don’t know how to pass that in. I tried typing 51 + angle(Mouse position), but when I press enter, “+ angle” clears out.
so this is my question, how do I pass Sword.Angle into that z rotation box?

For clarification, I know I can transform the parent position but my sword sprite looks bent out of shape
when my mouse position is to the left or right. That’s why i am resorting to this method