To Modify a Mill Surface
1. Select the name of the mill surface feature that you want to modify on the Model Tree. The current volume definition is displayed in red.
2. Do one of the following:
◦ Right-click and select Redefine Mill Surface from the shortcut menu. Creo NC activates the mill surface tool and enables the icons that are relevant for the selected mill surface. You can add features to the mill surface using this option.
◦ Right-click and select Edit Definition. Creo NC enables the tab for the feature that you selected.
Alternatively, you can use the > 
Operate > to add features to a mill surface.
Operate > to add features to a mill surface.