Post Carousel – Post Template

Sorry if I am missing where this is defined, or if it has been answered previously.

I’m looking at the Post Carousel block and under Display Settings see a select field for “Post Template”, I’m curious how I add custom templates to this area.

I’ve poked around trying to find the answer in docs and tried adding {theme}\getwid\post-carousel\custom-template.php with a Template Name comment in it, but I am having no luck. Can you point me in the right direction?