1. Go to Pages > All Pages.
2. Click on the page title that you wish to update, e.g. "Home".
3. Scroll down to the "Yoast SEO" title.
4. Click on the "Social" tab.
5. Upload your image under "Facebook Image" field, the recommended size is 1200px (width) x 630px (height).
6. Click "Update" once done.