Step 1. From the Admin Dashboard, go to Setup -> Settings, click on "Social Icons Settings".
Step 2. And then select the Referral Program.
Step 3. In the following page, check the box to enable the option and click "Update".
Step 4. Get into "www.wix.com" and login to the Wix account.
Step 5. After login, clikc on "Manage & Edit Site".
Step 6. Under Edit Site, click "Social", then upload the image and add the required Username for Facebook.