HRLocker reflects the date format of the browser you are using.
So if you are using Chrome with English (United States) chosen, the dates displayed in HRLocker will be American.
If you log on to a different browser, say Firefox set to English (United Kingdom), the dates displayed will be European.
So change your individual browser to reflect European date and HRLocker will automatically reflect this change.
To change the date format differs according to individual browsers but as a general guide..
Go to settings on the top right of your internet browser. When you click on settings scroll to the bottom and select advance settings. Click on languages and then add in English UK as an option. Drag English UK to the top of your language preferences displayed on the left.
On Mac, you go to Apple menu > System preferences > Region and Language and add UK English to the top of the list, then restart.