Can't find where to change the slug or delete the page with this URL

Hi there!

I have built a site for my father.

There is a page called https://perberger.se/bilder. But the exakt same page is also visible with the url https://perberger.se/bilder/1979/. I want to use that URL for another page but since it’s taken I can’t. When I try to edit https://perberger.se/bilder/1979/ (to try to delete this page) it goes to page https://perberger.se/bilder. I can’t find where to delete page https://perberger.se/bilder/1979, and I don’t know how it appeared on the site.

There is no pages in the trash. There is no category or tagg with the name 1979.

The site is in Under construction mode and hence only visible when logged in.

Best wishes Josefin