A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
In Windows, click the Start button and start typing set regional format.
You should soon see 'Set regional format' in the search results.
Click on it.
Does the 'Short date' format use - instead of / ?
If so, click 'Change data formats' and select a format using /
If that doesn't help:
You can force Excel to use / by clicking Custom in the Category list, and specify mm/dd/yyyy in the Type box.