Sure, I can definitely help you set up a countdown timer in Microsoft Excel. Here are the steps:

1. Open a new Excel workbook and create a new sheet.
2. In cell A1, enter the date you want to countdown to in the format of mm/dd/yyyy. For example, if you want to countdown to Christmas Day, enter 12/25/2021.
3. In cell A2, enter the formula "=A1-TODAY()". This will calculate the number of days between today's date and the date you entered in cell A1.
4. Format cell A2 as a number with no decimal places. To do this, right-click on cell A2 and select "Format Cells". In the "Number" tab, select "Number" as the category and set the decimal places to 0.
5. In cell A3, enter the text "Days Left". This will be the label for the countdown timer.
6. In cell A4, enter the formula "=IF(A20,A2,"0")". This will display the number of days left until the countdown date in cell A1. If the countdown date has already passed, the formula will display "0".
7. Format cell A4 as a number with no decimal places, just like you did with cell A2.
8. To make the countdown timer more visually appealing, you can add conditional formatting to cell A4. Right-click on cell A4 and select "Conditional Formatting". In the "New Formatting Rule" dialog box, select "Format only cells that contain" and set the rule to "less than or equal to" and "0". Then, choose a formatting style that will make the countdown timer stand out, such as a bold red font.
9. Save your Excel workbook and you're done! The countdown timer will update automatically every time you open the workbook or when the date changes.