1. Select the cell that contains the text you want to format.
2. Right-click on the cell and select "Format Cells" from the drop-down menu.
3. In the Format Cells dialog box, select the "Font" tab.
4. Check the box next to "Strikethrough" to apply the formatting to the selected text.
5. Click "OK" to close the dialog box and apply the formatting.

If the strike-through formatting still doesn't appear, try widening the cell to see if that makes a difference. You can do this by hovering your mouse over the right edge of the cell until the cursor changes to a double arrow, then clicking and dragging the edge of the cell to make it wider.

If you're still having trouble, it's possible that there is some other formatting applied to the cell that is overriding your strike-through formatting. Try selecting the entire cell and removing any other formatting (such as bold or italic) to see if that helps.

I hope this helps you get your formatting working correctly!