Open an Excel spreadsheet. Highlight the range of cells you want to search for duplicates. To highlight data, left-click at the top left of the first cell and drag the cursor to the bottom right of the last cell.
Click on the "Home" tab.
Click on "Conditional Formatting" in the "Styles" group.
Mouse over "Highlight Cells Rules" and then click on "Duplicate Values."
Click on the drop-down menu on the right to choose a highlight color, then click the "OK" button. Excel will highlight the duplicates in the cells you selected.