Subdomain – wp-blog-header.php issue

I just successful moved my blog [ https://www.example.com ] to [ https://subdomain.example.com ]. Now i want to make [ https://www.example.com ] my site address.How do i edit wp-blog-header.php for site url to work. Thank you so much.

<?php
/**
 * Loads the WordPress environment and template.
 *
 * @package WordPress
 */

if ( !isset($wp_did_header) ) {
	$wp_did_header = true;
	require_once( dirname(__FILE__) . '/wp-load.php' );
	wp();
	require_once( ABSPATH . WPINC . '/template-loader.php' );
}
?>