Allow me to join the thread, @DJH47.

Usually, QuickBooks uses the system date format from your Mac system preference. For now, let's try closing QuickBooks, then go into your System Preferences and change (toggle) the date format. Then close the system preferences and launch QuickBooks. 

If you feel uncomfortable uninstalling and reinstalling QuickBooks, I suggest reaching to our Support Team so they can check this further securely. To contact support, follow the steps provided above.

Get back to me if you have any other questions. I'm always here to help. Have a good day!