/**
 * @param array $defaults
 * @param string $method
 * @param array $args
 * @return array
 */
add_filter('site-reviews/defaults/reviews', function ($defaults, $method, $args) {
    $themeId = 21801; // change this as needed
    if ($themeId === (int) glsr()->args($args)->theme) {
        $defaults['orderby'] = 'random';
    }
    return $defaults;
}, 10, 3);