You can undo any changes and then redo them if you want.
Undo the last action: Choose Edit > Undo (from the Edit menu at the top of your computer screen), or press Command-Z.
Redo the last action you undid: Choose Edit > Redo (from the Edit menu at the top of your computer screen), or press Command-Shift-Z.
If you open an existing spreadsheet, edit it, then decide you don’t want to keep any of your changes, you can revert the spreadsheet to a previous version.