How to insert control points to a surface?

[hk11 (Hk)]

I want to run a function like the rhino command “_InsertControlPoint” but I can’t get a right way.
My code like below

var result= item.Surface().ToNurbsSurface().KnotsV.InsertKnot(0.5);

Even result is true but the surface didn’t add any control point. Pls, give me some suggestions, thanks.