Excerpt when sharing base URL defaults to last article

I’m trying to find out if there is a way to modify the excerpts behavior in the Freak Theme when simply sharing the root URL without an article/blogpost.

For example, when I share https://www.examplesite.com to facebook, I’d rather use the site summary as the excerpt for the site.

When I share https://www.examplesite.com/2017/05/03/complaining-about-freak-theme/, I would use the article excerpt.

Make sense?

Please tell me there is an easy way to accomplish this behavior.