To allow others to access and post on your page’s behalf, you must first give them admin access.
1. Navigate to Facebook.com, then click "Pages" on the left column.
2. Select your page
3. Scroll down on the left column and click “Settings”
4. Navigate to “Page Roles”
5. Under “Assign a new Page role”, type in the person’s name or the email address that’s associated with their Facebook profile.
6. Assign the appropriate page role.
7. Click “Add”
The person will receive a notification on Facebook or via email to confirm their role. Once they confirm, they will have access.