Underscore in my RapidWeaver blog URL

I’m trying to figure out how/why RapidWeaver is using an underscore in my URL. Below is an example “index_files” is what I’m trying to figure out. I’d like it to be a hyphen. Any thoughts? Thank you.

https://www.themillermachine.com/setup-shots/index_files/andy-blanco-an-american-in-paris.php