Go to www.facebook.com and Sign in.
Click on the “COG WHEEL“ and select your business page in the “Use Facebook as…” part.
Click on “EDIT PAGE” and then “ADMIN ROLES”.
Enter the “Facebook login email” of the person you want to add to your account. Select the appropriate privileges (see image for details). When you’re done, click “SAVE”
If it ask you to enter your password to continue, do so.
You’re done! The person should appear on the “Admin Roles” page. Make sure you gave that person the right privileges.