Freemius - Changing Search Permastruct

functions.php

<?php
/**
 * Customize docs search permastruct for search caching.
 *
 * @author Vova Feldman
 */
function freemius_docs_search_permastruct_rewrite() {
	if ( post_type_exists( 'docs' ) ) {
		/**
		 * We want the search pages to be cached.
		 */
		add_rewrite_rule(
			'^help/documentation/search/([^/]+)/?',
			'index.php?post_type=docs&s=$matches[1]',
			'top'
		);
	}
}

// The reason we use priority 20, is because this method must be triggered 
// after `remove_rewrite_rules()` of the docs CPT is called.
add_action( 'init', 'freemius_docs_search_permastruct_rewrite', 20 );