Page redirect in custom WebformHandlerBase
&lt;?php
namespace Drupal\sa_webform\Plugin\WebformHandler;

use Drupal\Core\Session\AccountInterface;
use Drupal\Core\Serialization\Yaml;
use Drupal\Core\Form\FormStateInterface;
use Drupal\webform\Plugin\WebformHandlerBase;
use Drupal\webform\webformSubmissionInterface;

/**
 * Form submission handler.
 *
 * @WebformHandler(
 *   id = "my_webform_handler",
 *   label = @Translation("My webform handler"),
 *   category = @Translation("Webform Handler"),
 *   description = @Translation("Calculate the score with webform 
 *                                                     submissions"),
 *   cardinality = 
 *       \Drupal\webform\Plugin\WebformHandlerInterface::CARDINALITY_SINGLE,
 *   results = 
 *    \Drupal\webform\Plugin\WebformHandlerInterface::RESULTS_PROCESSED,
 * )
 */

 class MyWebformHandler extends WebformHandlerBase {
 /**
  * {@inheritdoc}
  */
    public function submitForm(array &amp;$form, FormStateInterface $form_state, 
                           WebformSubmissionInterface $webform_submission) {

       $form_id = 'webform_submission_' . $webform_submission-&gt;getWebform()-
               &gt;id() . '_form';
       if($form_id == 'webform_submission_xxx_form') {
         $values = $webform_submission-&gt;getData();  
         /* Take the action based on the Webform submission values */   
       }    
    }

    public function confirmForm(array &amp;$form, FormStateInterface 
          $form_state, WebformSubmissionInterface $webform_submission) {
       $form_id = 'webform_submission_' . $webform_submission-&gt;getWebform()-
                                                  &gt;id() . '_form';
       if($form_id == 'webform_submission_xxx_form')
       {
          if(based_on_some_condition) {
          /* Here 12 is the node id where i wanted to redirect to */
          $form_state-&gt;setRedirect('entity.node.canonical',['node' =&gt; 12]);
       }
    }
}   
?&gt;


For more examples refer webform modules src code located at webform\src\Plugin\WebformHandler

BrokenWebformHandler.php

DebugWebformHandler.php

EmailWebformHandler.php

RemotePostWebformHandler.php