Cakephp 3.6：使用下拉列表和复选框创建新视图

I am building a task manager application and among other I have these tables:

TaskTypes : [id, name, instructions]

TaskElements : [id, name, description, task_type_id, element_category_id]

ElementCategories : [id, name]

In the TaskTypes view.cpt I want to create a button which will open a new screen where the user can select an Element Category from a drop down menu and then will see a table with all the TaskElements that belong to this Element Category. Each row (Task Element) will have a checkbox, so the user can select Task Elements and then with a Submit button the selected Task Elements will be duplicated with the task_type_id filled from the TaskTypes view.cpt.

Because I am fairly new to cakephp I have these questions:

How I can write the code to update the table based on the dropdown selection?

I have created these new files:

addelement\index.ctp and AddElementController.php:

AddElementController.php:

<?php
namespace App\Controller;

use App\Controller\AppController;

/**
* AddElement Controller
*/
class AddElementController extends AppController
{

     /**
     * Index method
     *
     * @return \Cake\Http\Response|void
     */
    public function index()
    {
        $elementCategories = TableRegistry::get('ElementCategories')->find('list', ['limit' => 200]);

        $this->set(compact('elementCategories'));
    }
}