Hi there! I can definitely help you with this problem. Here's a

1. Select the range of cells in column A that you want to compare with column B.
2. Go to the Home tab and click on Conditional Formatting, then select "New Rule".
3. In the "New Formatting Rule" dialog box, select "Use a formula to determine which cells to format".
4. In the formula bar, enter the following formula:
   Formula:

   =COUNTIF($B:$B,A1)0 

5. Click on the "Format" button and choose the formatting you want to apply to the cells that match.
6. Click "OK" to close the "Format Cells" dialog box.
7. Click "OK" again to close the "New Formatting Rule" dialog box.

This will highlight all the cells in column A that have a match in column B. You can then repeat the process for column B to highlight the cells that have a match in column A.

Note that this method will only work if the values in the two columns are exactly the same. If there are slight variations in the values (e.g. extra spaces), you may need to clean up the data first before comparing.