Step 1: Go to your Business Manager

Step 2: Click on your "Business Settings" button (top right corner)

Step 3: Once you are in your Business Settings, click on the "Partners" tab along the top of the window and then click on "Add New Partner."

You will see the following popup:

Step 4: You will have to enter our Business ID in that box:   1044585282290134

Step 5: Then, click "Next"

Step 6:  You will see a box like this one:

Step 7: You need to select the Facebook Page as well as the corresponding Facebook Ad Account, then click "Assign Assets"

Then, you should see something like this and you've completed the process. 

*Note: Please be sure we have Advertiser level permissions on both the Facebook Ad Account and Facebook Page.

Video Instructions

Additionally, you can also watch this video for instructions, "How to Assign a Partner on your Facebook Business Manager."  https://www.youtube.com/watch?v=FZQRGMFSjIA