<?php
add_filter( 'hsph_plugin_tagging_topics_post_types', 'register_custom_post_types_for_tagging' );

function register_custom_post_types_for_tagging( $post_types = array() ) {
	// Array of custom post types.
	$cutom_post_types = array( 'custom-post-type-slug1', 'custom-post-type-slug2' );
	// Merging default post types and custom post types.
	$post_types = array_merge( $post_types, $cutom_post_types );

  return $post_types;
}