You can access this tool from the following:
This tool removes 3D elements from a terrain which were added by Add Features or Create from Elements. The elements can be placed in a selection set prior to starting the tool, or can be selected individually within the tool.
Create a selection set with the elements to be removed.
Start the tool.
Specify a terrain model for which elements are to be removed.
Accept to remove the elements. The terrain is updated to reflect the removed elements.
Workflow - Without Predefined Selection Set