--Select the range of dates which needs to be corrected.
--From menu Data>Text to Columns will populate the 'Convert Text to Columns
Wizard' Hit Next>Next will take you to Step 3 of 3 of the Wizard.
--From Column Data format select Date and select the date format in which
your data is (MDY or DMY or what ever it is) .
--Hit Finish. MSExcel will now convert the dates to the default date format
of your computer.