/**
 * Set the Assigned Posts dropdown value from an URL parameter (?product_id=1)
 * Example: https://domain.com?product_id=26904
 * @param array $fields
 * @return array
 */
add_filter('site-reviews/review-form/fields/normalized', function ($fields) {
    foreach ($fields as $field) {
        if ('assigned_posts' !== glsr_get($field, 'field.type')) {
            continue;
        }
        if (!in_array('product', glsr_get($field, 'field.posttypes'))) {
            continue;
        }
        $postId = intval(filter_input(INPUT_GET, 'product_id'));
        if (empty($postId) || 'product' !== get_post_type($postId)) {
            continue;
        }
        $field->field['value'] = $postId;
        break;
    }
    return $fields;
}, 20);