Subscribed calender shows a non-existing holiday

I have the Swedish calender - it works well on all my units.

But where do I change one holiday that not exists? Or to whom do I tell that it should not be there?

It is "Whit Monday" (most people miss it and want it back, but government has diced).

From Google translate: In 2004, when the Parliament decided that the national day would be a holiday, which was otherwise abandoned as a red day in Sweden. It is not considered reasonable to introduce another holiday in the current economic situation without an existing holiday being removed or moved