Login to your Facebook account using your Login ID / Email ID & password
Login IDType Login ID
Password**********
Select the page who's access you want to give.
Click on the "Settings" tab present on top right corner of the selected page.
Under settings on left side, click on the "Page Roles" option as shown below
Under page roles you will get an option to enter the mail id of the user to whom you wish to grant access. Then click on "Add" button.
Once you click the add button, you will then be asked to re-enter your account password to confirm the request.
Once you confirm your password, that particular user will receive a notification to accept the request.
The user needs to check his notifications tab. Once he clicks on it, it will redirect to an invitation page. There, under "Pending Partner Request click on the "Accept" button to accept the page access request
Facebook Page Access Steps