To Undo the Last Operation
Do one of the following:
Note: For example, suppose that you just deleted an element with the Delete Element tool. To undo this operation, you would click the Undo icon on the Quick Access Toolbar.
Tip: If you hover the mouse over the Undo icon in the Quick Access Toolbar, it shows you the last command it will undo.
Tip: After you undo an operation, the operation just before it becomes reversible. You can, therefore, undo a series of operations by repeatedly clicking the Undo icon.