Setting Estlcam material thickness

Noob question. I’m trying to carve a 3D .stl file in Estlcam. The item is about 1/2 inch thick but the material I’m carving it out of is about 3/4 inch thick. How do I tell Estlcam to remove the 1/4" of material at the top so that I don’t have to spend an hour sanding it off the bottom to remove the part?

In the box that comes up in 3D mode there is one that says “shift downwards” hover over that and it should explain it pretty well.

Let me know how it goes.

ah! Brilliant. For some reason I assumed that meant moving it down as in the front of the material, not down like the bottom. Thanks