Currently the only way to delete a segment is with the undo feature while drawing the room. Once the room has been drawn however, there is no current way to delete a segment. You can undo as many points as you want to get back to the segment you wish to delete. We realize the importance of this feature and its on the way! Stay tuned for app updates.
You can however delete any structure you have drawn, such as a window or island at any time. Just hover over the structure and select the trashcan button.