C# - make polyline smaller

Hi, noob here.

I have a closed polyline, all the corners are 90 degrees to each other. I need to move all the x and z points 5 units towards the inside of the shape.

Is there an API call for this?
The other options seems to be loop through the points, figure out which way to move the point and move the point, write it back to the polyline.


Transform.Scale ?


Thanks. Offset did the trick