How do i add extra fields in magento 2 Core Review module Form

Use plugin for that.

Review Add Form
Now Create Form.php file in following directory
app\code\QaisarSatti\HelloWorld\Plugin\Adminhtml\Add

  namespace QaisarSatti\HelloWorld\Plugin\Adminhtml\Add;
  class Form extends \Magento\Review\Block\Adminhtml\Add\Form
  {
   public function beforeSetForm(\Magento\Review\Block\Adminhtml\Add\Form $object, $form) {
       $fieldset = $form->addFieldset(
           'review_custom',
           ['legend' => __('Review Custom Field'), 'class' => 'fieldset-wide']
       );
      $fieldset->addField(
           'test',
           'text',
           ['label' => __('Test'), 'required' => false, 'name' => 'test']
       );
      return [$form];
   }
}

Review Edit Form
Now Create Form.php file in following directory
app\code\QaisarSatti\HelloWorld\Plugin\Adminhtml\Edit

  namespace QaisarSatti\HelloWorld\Plugin\Adminhtml\Edit;
  class Form extends \Magento\Review\Block\Adminhtml\Edit\Form
  {
   public function beforeSetForm(\Magento\Review\Block\Adminhtml\Edit\Form $object, $form) {
      $review = $object->_coreRegistry->registry('review_data');
       $fieldset = $form->addFieldset(
           'review_custom',
           ['legend' => __('Review Custom Field'), 'class' => 'fieldset-wide']
       );
      $fieldset->addField(
           'test',
           'text',
           ['label' => __('Test'), 'required' => false, 'name' =>; 'test']
       );
      $form->setValues($review->getData());
       return [$form];
   }
}

Qaisar Satti

Hi, I'm Qaisar Satti! I've been a developer for over 20 years, and now I love sharing what I've learned through tutorials and guides. Whether you're working with Magento, PrestaShop, or WooCommerce, my goal is to make your development journey a bit easier and more fun. When I'm not coding or writing, you can find me exploring new tech trends and hanging out with the amazing developer community. Thanks for stopping by, and happy coding!