This is an extract from: https://support.wix.com/en/article/changing-your-social-share-image
Choose which thumbnail image to display when sharing your site on Facebook, Twitter or other social networks.
You can set a different social share image for each page of your site, or one image for the whole site.
To change the social share image for an individual page:
- Click Menus & Pages on the left side of the Editor.
- Click the relevant page.
- Click the Show More icon.
- Click SEO & Social.
- Click the camera icon.
- Select an image.
- Click Apply.
To change the social share image for your whole site:
- Go to Settings in your site’s dashboard.
- Click Social on the left.
- Click Upload Image.
- Select your image.
- Click Choose Image.
- Go back to the Editor or ADI and publish your site.