How do I reply using a file in Fiddler Everywhere Free?

I am trying to replace a production js file on a site with a local copy of it so I can set my own event listeners and control the layout of the page as needed. A lot of old stackoverflow answers suggest using fiddler to do that, but apparently the UI has changed since then. I have added the file I want changed to the autoresponder list but it does not have an option to return a file. The closest I've gotten is return a manual response which I have to copy and paste a 50k line javascript file every time. Can I get a more detailed explanation of how to do this in the new UI or was this removed from the free version of Fiddler Everywhere?