You need to connect more of your pages to ManyChat, but when you click "Add New Pages", you don't see other pages in the list of choices? It means that when you first connected your Facebook Account to ManyChat, you did not choose all of the pages that you manage on Facebook, but only a few of them.
To connect new pages to ManyChat, you have to be the Admin of these pages on Facebook (NOTE: 'Editor' role on FB is not enough to do that) - just click this button:
But if you do not see all of the pages, then follow these steps:
1. Follow this link https://www.facebook.com/settings?tab=business_tools
2. Find ManyChat in the list of apps at Facebook's Page Settings -->Messenger Platform and remove it.
3. Log into your ManyChat account again.
You won't lose any of your bot's settings or subscribers of course!
Please make sure that you re-connect all Pages that you're managing in your ManyChat account after deleting the app on FB and logging back into ManyChat.