Only show WooCommerce products in search results

Paste the following in functions.php:

add_action( 'pre_get_posts', 'wpse223576_search_woocommerce_only' );

function wpse223576_search_woocommerce_only( $query ) {
  if( ! is_admin() && is_search() && $query->is_main_query() ) {
    $query->set( 'post_type', 'product' );
  }
}

Source: https://wordpress.stackexchange.com/questions/223576/changing-a-themes-search-function-to-only-show-results-from-woocommerce