If you want to change the single page
page-{page-slug} is a good choice if you want the page template for specific page only and not multiple pages.
Check out his custom page template for specific page
If you are talking about custom post type
We can use single-$posttype.php , here $posttype is your custom post type slug.
WordPress template Hierarchy for single post page’s custom post is in the order of :
single-$posttype.php ==> single.php ==> singular.php(WP 4.3+)
So if a custom post single page is requested, WP first looks for single-$posttype file if it’s available it uses that file else it goes to single.php and so on as the above order.
Refer to Template Hierarchy for more details.