This script will filter default WordPress Search by the post type which you want to search for.

FilterWordPressSearch.php

<?php
/**
 * Filter WordPress Search for specific post types
 *
 * @param $query
 *
 * @return mixed
 */
function bloggerpro_only_post_search( $query ) {
  if ( $query->is_search ) {
		$query->set( 'post_type', 'post' );
	}
	return $query;
}

add_filter( 'pre_get_posts', 'bloggerpro_only_post_search' );