ExampleConfigEntityExistingForm.php

<?php

namespace Drupal\ctools_wizard_test\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Simple wizard step form.
 */
class ExampleConfigEntityExistingForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'ctools_wizard_test_config_entity_existing_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form['existing'] = [
            '#markup' => '<p>This step only shows if the entity is already existing!</p>',
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        // Do nothing!
    }

}