Is there a way to get page permissions back?

C5 newbie. Inherited this live site--no dev environment. C5 version 5.5.1. My user is in the Administrator Group.

I was having trouble editing a page's content and tried changing the page's permissions. Set the page's "Assign Permission" control to "By Area of Site (Hierarchy)." Little did I realize, my user has no permissions based upon that "area" of the site. And now an entire branch of the site is read-only for me. It's beyond me how/why an "area of the site" could even be set to deny editing access to the Administrator Group, from Home page to every leaf page on the branch. But that's apparently what is.

So, how can I get permissions back?

Thanks in advance.