You want (probably) add_submenu_page
. The first parameter– the one listed as $parent_slug
in the Codex is going to be edit.php?post_type=your-post-type-name
, like this (mostly cribbed from the Codex page):
function add_submenu_wpse_81844() {
add_submenu_page(
'edit.php?post_type=your-post-type-name'
, 'My Custom Submenu Page'
, 'My Custom Submenu Page'
, 'manage_options'
, 'my-custom-submenu-page'
, 'my_custom_submenu_page_callback'
);
}
add_action('admin_menu', 'add_submenu_wpse_81844');
Check the Codex for what the other parameters mean.