Crop an object with the Trim tool . This displays a trim box that deletes any 3D data outside the box.
Open the Trim tool by tapping the Edit button, then tapping Trim.
Tap and drag the handles on the trim box to make it larger or smaller. If you cut into the object you will start to see it grey out.
Tap the Save button when you’re finished.
Save the trimmed scene with a new file or overwrite the original model.
Rotate the scene before you save it to make sure the front, back, top and bottom faces of the box are positioned properly.
The bottom of the trim box is always parallel to the ground. Rotate it by dragging it with one finger.