Unfortunately, Facebook no longer allows passing the image that you want through share buttons, instead, they are all defined in the header via og:image tag. You can add this tag manually or through a plugin:
1. Manually: If for some reason, you are not using SEO by Yoast, you can manually add og:image tag by following the second section of this tutorial.
2. Via SEO by Yoast plugin: In SEO by Yoast, the most popular WordPress plugin for SEO, you can define which image to share by following this tutorial: https://kb.yoast.com/kb/why-doesnt-facebook-display-an-image/
Depending on which page your customers are sharing, you need to set up an image for that page. So if in plugin settings, you defined that the My Account page referral link will be the home page, then you need to set up a social image on the home page. In order to test which image is sharing for you, you can use this debugger tool. Just click Scrape again if you replace the image and you don’t see a new one appearing.