Is it possible to duplicate a face?

In the construction of my toaster, after having made this part (green arrow), it is in external volume + chamfer ; I would have liked to put it a little further back to form a hollow.

In the mesh (blender), I copy the face and I push it backwards.
In Sharp, this reduces my whole shape towards the back.

Sorry, my English is a bit poor for this kind of explanation.

Thanks for your answer.