Featured image for homepage / frontpage

Hello, I know how to set a featured image to be shared with a post or page. My homepage is a list of recent posts. How do I set the featured image for my homepage? I have spent over an hour searching Appearance/Customise and the Internet and Support Forums for how to do this. I want to set the image that is shared when I share www.myhomepage.com (Website is www.thechurning.net) MANY THANKS :o) Finn