How to crop 3D model with swift?

I want to crop the usdz model in runtime. I use ModelIO for this.

Before: [https://i.stack.imgur.com/yDXXF.jpg)

After: [https://i.stack.imgur.com/m9ryg.jpg)

First of all, get file from bundle

        let url = URL(fileURLWithPath: file)     
    } else {
        print("Object not found in Bundle")
    }

And then I need to access asset

let asset = MDLAsset(url: url)

What should I do after this step? How am I supposed to use SCNGeometrySource and SCNGeometryElement or MDLVoxelArray classes?