After selecting the "Location" tab in the Settings page, select the location you want to edit and click the "Edit" button.

Scroll to the Holiday section of your Location and enter the name of the Holiday you wish to add in the "Name" field. Next, select the date of the holiday by clicking in "Date" field and the select the correct date by using the calendar. When you are done, click on the "Add" button to add the new holiday to the list of holidays for your Location.

Don't forget to click the "Save" button at the bottom of the page to confirm your changes.