How to set Noindex to all wordpress pages in a catergory?

As the previous code I posted didnt work for the OP, clutching at straws, we can try to obtain the same outcome using get_the_category
As the OP stated he was using YOAST, i’ll wrap this function into the YOAST hook for robots.

add_filter('wpseo_robots', 'yoast_no_home_noindex', 999); 
function yoast_no_home_noindex($string= "") {
   $term_id = get_the_category( $post->ID );
      if($term_id[0]->term_id == 92) {
         $string= "noindex, nofollow";
      }
      return $string; 
}

Same again, just drop this into your themes functions file.