Copy to you themes template, update the name of the CPT as required.
<?php
global $post;
if ( isset ($post) ){
$post_parent = $post->ID;
if ( !empty($post->post_parent) ){
$post_parent = $post->post_parent;
}
$args = array( 'posts_per_page' => -1, 'post_parent' => $post->post_parent, 'post_type'=> 'custom-post-name' );
$myposts = get_posts( $args );
foreach ( $myposts as $post ) : setup_postdata( $post ); ?>
// html content
<?php endforeach;
wp_reset_postdata();
}
?>