Add content area to custom post type

I’m hacking up a built-in photo gallery to serve as a pro wrestling roster section. I have the gallery working as I’d like (https://inspireprowrestling.com/talent-roster/) but I’m running into lots of problems with the ‘profile’ pages.

The theme I’m using is called “Iron Band” and they have a custom post type called “single-photo”… But I’m not able to get a content area on it. I’ve tried plugins for custom fields and I’ve tried copying the regular single-post.php code, but I never get an editable text area in the backend editor. With the More Fields plugin, I can see a field in the editor, but nothing I put in there appears on the post.

Here’s an example of the posts: https://inspireprowrestling.com/photo/andy-dalton/

Any idea how I can add a text area to this post type?