Display Modified Author

We use this plugin to display custom post types to the front end, but allow admins to see extra content, like when it was last modified, provide a link to edit, ect. We have multiple users editing and reviewing content. We’d like them to be able to see who last edited a given page/post. Found that WordPress has a the_modified_author() function. Tried dropping this into the [loop] with no luck. Tried [field the_modified_author], [field modified_author], [field=the_modified_author], [field=modified_author], [field modified-author], etc. I’m assuming it isn’t present as a feature. If it is, how can I call it? If not, could it be added?