Copy usermeta value where ID matches in the same table

use this code, it may help you

 $users = get_users($args);
      if($users) {
        foreach($users as $user) {
            $user_id = $user->ID;
            $shipping_first_name = get_user_meta($user_id, 'shipping_first_name', true);
                if($shipping_first_name) {
                  update_user_meta( $user_id, 'first_name', $shipping_first_name);  
                }
            }
        }

for $args – refer link https://codex.wordpress.org/Function_Reference/get_users