If you need someone to manage your Facebook page, it’s best to give them access to manage it than give them your personal username and password. Here are the steps on how to give other users access to manage your Facebook page.
Users who have liked the page are the only ones that are allowed to be added as a moderator of that page.
1) Log into Facebook and go to your Facebook page.
2) Click on the Settings > Page Roles.
3) Put the name or email address of that person in the box shown in the picture.
Which role would you like to assign this person? Here is a table to help you decide.
Once you hit save at the bottom, the person invited will receive the notification that they have been given access to that page.