course and forums are connected then course author,reply author and topic author can see private replies.

course user see reply

if(!empty($GLOBALS['bbp_private_replies'])){
	//settings in course settings page
	add_filter('wplms_course_creation_tabs','add_in_front_end');
	function add_in_front_end($settings){
		$fields = $settings['course_settings']['fields'];
		$arr=array(array(
			'label' => __('Course Students can see forum private reply','wplms-front-end'), // <label>
			'desc'  => __('Course Students can see forum private reply','wplms-front-end'), 
			'text'=>__('Forum private reply','wplms-front-end' ),// description
			'id'  => 'vibe_forum_private_reply_view', // field id and name
			'type'=> 'switch',
			'default'=>'H',
			'options'  => array('H'=>__('disable','wplms' ),'S'=>__('enable','wplms' )),
			'style'=>'',
			'from' => 'meta'
		));
		array_splice($fields, (count($fields)-1), 0,$arr );
		$settings['course_settings']['fields'] = $fields; 
	return $settings;
	}

	//Check for private if course forum setting enabled 
	//  then course users who are topic author / reply author / course course
	// can see course forum's topic's private reply
	add_filter( 'bbp_get_reply_content', function($content='',$reply_id=0){
		$bbp_private_replies = $GLOBALS['bbp_private_replies'];
		if( empty( $reply_id ) )
			$reply_id = bbp_get_reply_id( $reply_id );

		$content = get_post_field('post_content', $reply_id);

		if( $bbp_private_replies->is_private( $reply_id ) ) {
	
			$can_view     = false;
			$current_user = is_user_logged_in() ? wp_get_current_user() : false;
			$topic_author = bbp_get_topic_author_id();
			$reply_author = bbp_get_reply_author_id( $reply_id );
			

			if ( ! empty( $current_user ) && $topic_author === $current_user->ID && user_can( $reply_author, $bbp_private_replies->capability ) ) {
				// Let the thread author view replies if the reply author is from a moderator
				$can_view = true;
			}
	
			if ( ! empty( $current_user ) && $reply_author === $current_user->ID ) {
				// Let the reply author view their own reply
				$can_view = true;
			}
	
			if( current_user_can( $bbp_private_replies->capability ) ) {
				// Let moderators view all replies
				$can_view = true;
			}
			
			
			if( ! $can_view ) {
				$forum_id = get_post_meta($reply_id,'_bbp_forum_id',true);
				global $wpdb;
				$course_id = $wpdb->get_var($wpdb->prepare("SELECT post_id FROM {$wpdb->postmeta} WHERE meta_key='vibe_forum' AND meta_value = %d",$forum_id));
				$course_ids = array();
				if(!empty($course_id) && !is_array($course_id)){
					$course_ids = (array)$course_id;
				}else if(!empty($course_id) && is_array($course_id)){
					$course_ids = $course_id;
				}
				if(!empty($course_ids) && is_array($course_ids)){
					$topic_id= bbp_get_reply_topic_id($reply_id);
					$topic_author_id = bbp_get_topic_author_id( $topic_id );
					foreach ($course_ids as $key => $id) {
						if(bp_course_is_member($id,$current_user->ID)){
							$vibe_forum_private_reply_view = get_post_meta($id,'vibe_forum_private_reply_view',true);
							if($vibe_forum_private_reply_view == 'S'){
								$course_author = get_post_field('post_author',$id);
								if ( ! empty( $current_user ) && $course_author === $current_user->ID ) {
									// Let the course author view private reply
									$can_view = true;
									break;;
								}
								if ( ! empty( $current_user ) && $topic_author_id === $current_user->ID ) {
									// Let the topic author view private reply on their topic
									$can_view = true;
									break;;
								}
							}
						}
					}
				}
			}
			
			if(!$can_view){
				$content = __( 'This reply has been marked as private by  wplms.', 'bbp_private_replies' );
			}
		}
		
		return $content;
	}, 1000, 2 );
}