1. Navigate to the following directory in your cpanel or FTP: wp-content/themes/themeXXXXX/includes, locate a custom-function.php file, and click an Edit button (or edit it with the help of a text editor):
  2. Paste the following piece of code to the bottom of the file before the last ?>
  3. add_filter( 'woocommerce_get_catalog_ordering_args', 'custom_woocommerce_get_catalog_ordering_args' );

function custom_woocommerce_get_catalog_ordering_args( $args ) {
$orderby_value = isset( $_GET['orderby'] ) ? woocommerce_clean( $_GET['orderby'] ) : apply_filters( 'woocommerce_default_catalog_orderby', get_option( 'woocommerce_default_catalog_orderby' ) );

if ( 'random_list' == $orderby_value ) {
$args['orderby'] = 'rand';
$args['order'] = '';
$args['meta_key'] = '';
}
return $args;
}

add_filter( 'woocommerce_default_catalog_orderby_options', 'custom_woocommerce_catalog_orderby' );
add_filter( 'woocommerce_catalog_orderby', 'custom_woocommerce_catalog_orderby' );

function custom_woocommerce_catalog_orderby( $sortby ) {
$sortby['random_list'] = 'Random';
return $sortby;
}[*]
  4. Save the changes and navigate to the following directory in your WooCommerce Settings: Products–>Display:
  5. Check out the Random option under Default Product Sorting directory: