How to update a menu link in drupal 7 using hook n update

update_main_menu_using_hook_n_update.php

/**
 * Update we chat link inside menu social.
 */
function YOUR_THEME_main_menu_update_7004() {
  $id = db_select('menu_links', 'm')
    ->fields('m', ['mlid'])
    ->condition('menu_name', 'menu-social')
    ->condition('link_title', 'WeChat')
    ->execute()
    ->fetchCol();

  if (count($id) == 1) {
    $item = menu_link_load($id[0]);
    $item['options']['attributes']['class'][] = 'qr-link';
    menu_link_save($item);
  }
  else {
    throw new DrupalUpdateException('Could not find menu link to update.');
  }
}