Trim dialog box

Trims surfaces by removing the selected areas.

Access
Ribbon: 3D Model tab Surface panel Trim
Cutting Tool
Selects geometry used to trim the surface.
Remove
Selects one or more areas to remove. Click Remove, select areas to remove, then click OK.
Invert selection
Reverses the selection set (cancels the currently selected areas and selects the canceled areas). Surfaces that have no areas selected are not affected.