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Whilst being logged as an Jira's HR group user, from Navigation Bar Menu go to Management (1) ➜ Holiday Schemes (2). Now you can access scheme's name to edit it, (3) or To make changes, click on click "Edit" hyperlink (3) - both actions have the same effect.
Edition button for a holiday scheme is also visible after accessing/editing clicking on a desired scheme's name. If you do not wish to go with creation of new holiday schemes and assign particular users to it, then fast track mode is enough for you (i.e. working only on Default holiday scheme). In such case, then you can may use "Add holiday" button (5) to add off-work day to the calendar.
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