Laravel Eloquent update created_at value

I need to change a post created_at because i send sms to posts created at this month according to created_at. When i try with this created_at does not change value!

public function Controller(Posts $post){
    $post->update(Carbon::today());
}

from Newest questions tagged laravel-5 - Stack Overflow http://ift.tt/2sZBW7P
via IFTTT