custom navigation for organize series (pagination by series part) this can be added to the themes functions.php file

orgseries-custom-nav.php

add_action( 'the_content', 'os_custom_series_nav_filter' );

function os_custom_series_nav_filter($content) {
	global $post;
	if ( is_single() ) {
		$series = get_the_series();
		if ( !empty($series) ) {
			$cur_id = $post->ID;
			$posts_in_series = array();
			$result = '';
			$content .= '<div class="custom-series-navigation"><ul>';
			foreach ( $series as $ser ) {
				$series_id = $ser->term_id;
				$series_posts = get_objects_in_term($series_id, 'series');
				$posts_in_series = get_series_order($series_posts, '', $series_id, false);
				foreach ( $posts_in_series as $series_post ) {
					if ( $series_post['id'] == $cur_id ) {
						$content .= '<li class="custom-series-nav-current">' . $series_post['part'] . '</li>';
					} else {
						$content .= '<li><a href="'.get_permalink($series_post['id']).'" title="'.get_the_title($series_post['id']).'">'.$series_post['part'].'</a></li>';
					}
				}
			}
			$content .= '</ul></div>';
		}
	}
	return $content;
}