Set Page Parents of CPT | WP

functions.php

<?php
// Set page parents of Custom Post Types - in the Organisation Setting ACF Options page
// Based upon Joe Sexton's blog post http://www.webtipblog.com/setting-wordpress-custom-post-type-parent-specific-page/

function mpc_cpt_parent_page( $data, $postarr ) {
    global $post;

    // Verify if this is an auto save routine.
    // If it is, our form has not been submitted - so we don't want to do anything
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
        return $data;
    }

    if ( $post->post_type == "my-custom-post-type" ){
	    $data['post_parent'] = 1337;
	}

    return $data;
}

add_action( 'wp_insert_post_data', 'mpc_cpt_parent_page', '99', 2  );