I need to manage this page, but though I have logged in with the account that is supposed to be associated with it, I cannot post updates for that account.
The only person that can remove managers from a page is the owner, and there isn't a way to find who the page's owner is. You could attempt sharing privately with the page and see if you get a response. If you're unable to resolve this, the only option is to create a new page and report the old one for impersonation.
Add a comment...