How to find a point on polyline volume entity when start point and distance from start point is given?

Hello team,
I have extruded the polyline volume along the cartesian coordinates giving it the curve look.
I want to find the point at some distance from say any point on the polyline volume.

is it possible ?
I have given a normal flow of how I am creating the polyline volume sandcastle.

Sandcastle link

thanks !!