Deleting all entries in Evolution calendar

I am migrating to Linux KDE and Evolution and imported items into Calendar. By mistake, I pressed backspace on an Apple keyboard, which created an event I cannot delete. I imported an external calendar with 3 thousand events, I tried purging all events older than 1 year, but I get this error:

I got the same error when I tried to delete the event created by the backspace key.

How can I delete all calendar events (which I will then import again)?