404 dosya adınız 404.php ise:
<?php if(basename($_SERVER["SCRIPT_FILENAME"]) == '404.php'): ?>
<meta name="robots" content="noindex" />
<?php else: ?>
<meta name="robots" content="index, follow, max-image-preview:large, max-snippet:-1, max-video-preview:-1" />
<?php endif; ?>