Unsubscribe Landing Page is not Visible in Design Studio > Landing Page

Hi All,

I was reading this post about Unsubscribe Link in Marketo. From this post, it looks like we can edit the Unsubscribe Landing page that is supposed to be located in Design Studio > Landing Page. However, I do not see it there or anywhere else. When I tried to create the Landing Page with the name of UnsubscribePage which makes the URL ends with /UnsubscribePage.html, the system gives me an error saying "A page with that URL path already exists; please choose another path". Has anyone encountered the same issue before? Where can I possibly located the unsubscribe landing page?

Best,

Calvin