There are a few ways to add leading zeroes in Excel. One way is to use the text function. To do this, type "=text(A1,"000")" into a cell where you want the leading zeroes to appear, and replace "A1" with the cell address of the cell that contains the number you want to format. This will add leading zeroes to the number in the cell so that it has three digits.

Another way to add leading zeroes is to use the format cells function. To do this, type "=format cells(A1,"0")" into a cell where you want the leading zeroes to appear, and replace "A1" with the cell address of the cell that contains the number you want to format. This will add leading zeroes to the number in the cell so that it has the number of digits you specify.