If you have accidentally excluded a smart tag from your Excel spreadsheet, there is a way to undo the exclusion. Here's how:

1. Open the Excel spreadsheet that contains the smart tag exclusions.
2. Click on the File tab in the upper left-hand corner of the screen.
3. Click on Options in the drop-down menu.
4. Click on Proofing in the left-hand column.
5. Click on the AutoCorrect Options button.
6. Click on the Smart Tags tab.
7. Click on the Exceptions button.
8. Uncheck the box next to "Exclude from automatic smart tags."
9. Click on OK to save your changes and close the dialog box.