How To Use Undo & Redo Buttons
Making mistakes is common. If this happens, don't worry. You can use the Undo and Redo buttons to restore your drawing to its original condition.
To undo a mistake, just press the Undo button. If you'd like to undo multiple actions, continue to click the Undo button until you're satisfied with your drawing's appearance. Undo is often more convenient than trying to delete an item that you have accidentally drawn.
If you undo too much, then you can click the redo button in order to recover what you accidentally undid.
Note: This video has no sound; it has captions pointing out the relevant steps (program version 2.1).