Select the cells containing the dates
Right-click and choose Format Cells
Go to the Number tab
Select Date from the Category list
Choose the date format you want
Click OK
Alternatively, use the Home tab
In the Number group, open the drop-down list
Select Short Date or Long Date
To create a custom format, choose Custom in Format Cells
Enter a format code such as dd/mm/yyyy or mm-dd-yyyy
Click OK