Register Custom Post Type for Existing Plugin

I’m setting up appointment booking for a salon. The quality of the plugins I’ve tested have left much to be desired. I’ve found one that I might be able to make work ( plugins/salon-booking-system/ ) but the layouts are ugly. I want the services list to match my site design. The easiest way to accomplish this is to generate the list with a query loop block. With query loops, I can easily style the services list any way I want. Problem is the post type that salon-booking-system created is not registered as a CPT. What’s the easiest way to make a post type for an existing plugin show up in the query loop block editor?