The procedure to add national bank holidays is explained in section 2.2.1 of the software manual.
If you want to add a national holiday that was not included in the downloaded days:
1. Open the Planning page.
2. Set the Planning Mode to All.
3. Right-click on the day you want to set as a bank holiday.
4. Select "Add new".
5. Make sure that you link your new planning event to the Holiday work code.
If you want to delete a national holiday, follow these steps:
1. Open the Planning page.
2. Set the Planning Mode to All.
3. Right-click on the bank holiday you want to delete.
4. Select "Delete".
5. Confirm your choice.