You can modify
a surface boundary using its control points. You can deform the boundary by pulling the control point or the mesh line at that point.
Before you begin: Open an existing 3D shape.
Select the surface boundary you wish to edit.
From the Edition section of the action bar, click Control Points.
Control points and lines are displayed along that boundary.
Important:
By default all
control points are selected.
Click a specific point to deform the boundary at this point
only, or select a set of points using the Ctrl-key or
Shift-key while clicking (multi-selection capabilities).
Modify the boundary pulling on its control points or the
mesh line.
Click OK in the Control Points dialog box.
The boundary is modified.
Important:
Only the boundary and its control points are modified. Any other
boundary of the surface is not affected by these modifications.
See also Using Control Points.