Floating Island

Hi! Im trying to make a survival based game on a floating island. The one problem I have run into so far is how do I make a floating island. It seems as when I generate a plane of terrain its flat and I cant make it circular which is ok as long as I can make a floating island above it and then get rid of the rest of the terrain below. I can’t seem to find how I remove terrain as it only seems to build and the only way to remove is by Ctrl+Z so if anyone has any tips or tricks they would be greatly appreciated thanks! :smiley: ~CreativeBuilds