Although editing a worksheet is supposed to improve it, you might find that you've done something to a cell or range of cells that you had not intended. This is where the Undo feature comes in.
You can undo just about any action while working in Excel, including any changes you make to a cell's data. To undo a change, click the Undo button on the Standard toolbar (or select Edit, Undo ).
You can also undo an undo. Just click the Redo button on the Standard toolbar.