Non working days are available to be accessed by a Jira administrator. To do so, simply start typing "non working days" in a search field.
To add new non working day select type, name, date and then click on the "Create" (1) button:
When creating (1) a non working day you can specify its type, name and calendar date. Any added element here can be amended, or deleted, by using dedicated menu tied to each item (2). To find any already existing day, by searching its (partial) name, date, or type you can use filter field (3).
Important thing to note here is that it is up to you to decide of a "Type" of a non-working day