How to Set Regional Dates in Excel 2013
Click the Date tab in the Customize Format dialog box. Click the Short Date format and then type D/m/yyyy, the new date format.
You have to type this European date format because the United States regional settings don’t automatically include this format in the Short Date Style drop-down list. After manually entering this format, the European date format becomes part of the list that you can then select from in the future.