contacts_events-8.x-1.x-dev/modules/accommodation/contacts_events_accommodation.install

<?php

/**
 * @file
 * Install, update and uninstall functions for the accommodation.
 */

use Drupal\Core\Entity\Entity\EntityFormDisplay;

/**
 * Implements hook_install().
 */
function contacts_events_accommodation_install() {
  /** @var \Drupal\Core\Entity\Display\EntityFormDisplayInterface $display */
  $display = EntityFormDisplay::load('contacts_event.default.default');
  if ($display && $field_group = $display->getThirdPartySetting('field_group', 'group_booking_settings')) {
    $field_group['children'][] = 'accommodation_types';
    $display->setThirdPartySetting('field_group', 'group_booking_settings', $field_group);
    $display->save();
  }
}