add_filter('site-reviews/review-form/fields', function ($fields, $args) {
    $fieldName = 'description'; // change this to match the field name!
    $formId = glsr_get($fields, 'form.value');
    $type = glsr_get($fields, $fieldName.'.type');
    if (27291 == $formId && 'textarea' === $type) { // make sure we are using the relevant form
        $fields = glsr_set($fields, $fieldName.'.minlength', 10); // require minimum of 10 characters
    }
    return $fields;
}, 20, 2);