using appointments+ – can't select providers or services pages

I am using a theme for a beauty salon. The theme uses custom post types for the services and stylists. As a result, when I am configuring the appointments+ plugin (which I love BTW) by trying to associate a specific page with each provider or service, I can only select from the “Standard” pages in the drop-down, not the custom page types. I’m sure this is an easy customization, but it is beyond what I have done in WP prior to this. Can you point me in the right direction? Is there a snippet of code that I can edit so that the drop-down will also populate these custom post types?