How to call function from custom helper ?

On codeigniter 4.3.7 site I need to create a custom helper so I created a file app/Helpers/helper.php with code:

PHP Code:

<?php

namespace App\Helpers;

const DATE_FORMAT = '%B %d, %Y';

function formatDateTime($DateTimeLabel = '', $format = '')
{
... 


I try to call this method from view file app/Views/admin/categories/index.php:

PHP Code:

<?php helper('helper'); ?>
<?= $this->extend("layouts/default") ?>

<?= $this->section('content') ?>

<td><?= formatDateTime($category['created_at'], "ASTEXT") ?></td> 


But I got error that function formatDateTime not found even after in app/Config/Autoload.php I added ref to my helper file :

PHP Code:

public $helpers = [
'app/Helpers/helper.php'
]; 


Have I to run some console commands to use my helper ?

Thanks in advance!