This problem can arise if you have created a Facebook Group that exists within a Facebook Page. By default Facebook does make your personal Profile the admin, it makes the Facebook Page admin of the group. So if you are having trouble being able to post or change settings in your group, make sure you are the admin by following these steps:
• Login as your Page on Facebook
• Navigate to "Groups you Manage"
• Click on the "Members" Tab
• You should see your Profile in the list of Members
• Click the 3 dot icon to the right of your name
If you don't see your profile here, it means you haven't added yourself as a member to this group. Make sure to join the group.
• Choose "Add as Admin" from the popup menu
