Not 100% sure I follow the question. Are you asking what is the best way to recover a page (don't have the login information), or are you asking how to get access to a page once you've been granted manager access? If the client gave you manager access, you should receive a email notifying you.
I would try to have him give you access again just to make sure there is no operator error. If you still don't receive access I would use join.me to show them how to do it and then you can watch them do it. What also works is asking for access via the Google help page and they will send your client detailed info on how to grant access. As a last ditch effort, I would try getting the client on the phone with a Google rep. Hope one of these methods helps.
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