kommonikation on "Events Manager booking fields required"

Hi. I know that there are several forum posts about that - and I read them all. But they confuse me and I coudnt fix my problem. So I startet a new topic.

I am not using the EM pro. I want to set all of my booking fields als required fields. How to do that?

Somebody in a forum posted this snippet.

function em_validate($result, $EM_Event){
 if (!is_user_logged_in() && $_REQUEST['user_name'] == ''){
  $EM_Event->add_error('guest name is required...');
  $result = false;
 }
 retu $result;
}
add_filter('em_event_validate','em_validate', 1, 2);

But where to put? In which file?

Does anybody has another idea to set booking fields required?

Thanks for help.

WordPress ...