Changing date when format cells does not work

[Hapdawg88]

I downloaded some data from a data base and the dates are formatted: year-month-day: 2019-3-10. I attempted for re-format via format cells but it does not work. Any advice for how I can get these dates formatted: month-day-year: 5-13-2019?

Thank you for your help.

 

[Joe4]

If formatting does not have any affect, then it usually means that those values are entered as Text and not as Dates.
It is easy to convert ny highlighting the column, going to "Text to Columns" on the data menu, and on the third step, select Date with the YMD option, and then click Finish. This will convert the values to dates.
They will probably show up as large numbers (since dates are really just formatted numbers). To see the format you want, then apply your custom date format of M-D-YYYY.