How to modify the In-Content Related Post image loop by using the filter

add_filter('ampforwp_modify_inline_rp_loop_image','dummy_function');
function dummy_function($args){
    $thumb_url_2 = ampforwp_get_post_thumbnail('url');
    list($width, $height) = getimagesize($thumb_url_2);  

   $custom_img = preg_replace(
     '/<amp-img src=(.*?)\s(.*)width=(.*?)\s(.*)height=(.*?)\s(.*)layout=(.*?)\s><\/amp-img>/',
      '<amp-img src='.$thumb_url_2.' width='.$width.' height='.$height.' layout="responsive" class="img-cover"></amp-img>', $args);
    

  $custom_changes .= '<div class="image-container-rltd">';
  $custom_changes .= $custom_img;
  $custom_changes .= '</div>';
  $args = $custom_changes;
  return $args;
}