If during adding Facebook pages to LiveAgent you can't see all the pages where you are the admin, it is recommended to remove the LiveAgent from your Facebook business integrations, and then try to add the pages again.
First open your facebook and log in. Then open dropdown menu under the arrow in top right hand corner of screen, and click Settings.
In Settings select Business integrations category in the left hand side column.
Then select the LiveAgent business integration (or your own Facebook app integration if you're a downloadable license owner) and click Remove.
Then go back to your LiveAgent and try to connect your Facebook pages again.