Use Undo to reverse the last action. Unlimited Undos are possible. Every time you use Undo, the previous action is reversed. If you are not satisfied with the result of the Undo, you can use Redo.
Note: The Zoom commands cannot be reversed using Undo.
Click Actions on the toolbar and choose Undo.
Choose Edit > Undo.
Press ⌘Z
Control–click and choose Undo.
Note: When using Undo from the Edit menu, the name of the specific action to be undone is listed.