Activate the Extrude command and click on the top face of the part geo-
Draw a closed sketch on the top face.
On the ribbon, click Home > Sketch > Finish .
On the Extrude dialog, click End > Until Next . Under the Direction sec-
tion, click the Reverse Direction button.
Under the Boolean section, click Boolean > Subtract . Click OK to create
the cutout feature until the surface next to the sketch plane.