If you've accidentally added a public holiday to the calendar, you can remove it.
Click your name in the top right, then click Settings.
On the settings menu, click Calendar, then click Public holidays.
Click the pencil icon next to the public holiday that you want to amend
You can edit the following:
Date
Whether you want it to repeat on the calendar each year
Name
Allowance count setting, for example, if you want it to count against the employee allowance
Holiday groups you want to assign this public holiday to
Click Create to save your changes.