How to make block recession bone model

Hello, I am a beginner with 3D Slicer. I want to create a model for FEM analysis where the patellar groove has been block recessed. This model should have a block-shaped cutout in the groove. I would like to adjust the depth of this block as I create the model. What method should I use to create a segment in the bone where only this part is removed in a block shape?