Add data to file in Prestashop Feeder - php

Question

I'm trying to add this code:
$date = date('r', strtotime($product['date_add'])); echo '<pubdate>'.$date.'</pubdate>';
to rss.php file in Prestashop Feeder module https://github.com/PrestaShop/feeder
in order to have all products in Mailchimp rss email (now it shows just one because is missing date reference)
But I don't know where to add it.
class Ps_FeederrssModuleFrontController extends ModuleFrontController
{
private function getProducts($idCategory, $nProducts, $orderBy, $orderWay)
{
$category = new Category($idCategory);
...
);
}
}
return $productsForTemplate;
}
private function getSmartyVariables()
{
$id_category = (int)Tools::getValue('id_category');
$id_category = $id_category ? $id_category : Configuration::get('PS_HOME_CATEGORY');
$number = (int)Tools::getValue('n', 4);
$number = $number > 4 ? 4 : $number;
$orderBy = Tools::getProductsOrder('by', Tools::getValue('orderby'));
$orderWay = Tools::getProductsOrder('way', Tools::getValue('orderway'));
$products = $this->getProducts($id_category, $number, $orderBy, $orderWay);
return array(
'products' => $products,
'currency' => new Currency((int)$this->context->currency->id),
'affiliate' => (Tools::getValue('ac') ? '?ac=' . (int)Tools::getValue('ac') : ''),
'metas' => Meta::getMetaByPage('index', (int)$this->context->language->id),
'shop_uri' => Tools::getShopDomainSsl(true, true) . __PS_BASE_URI__,
'shop_name' => Configuration::get('PS_SHOP_NAME'),
'shop_email' => Configuration::get('PS_SHOP_EMAIL'),
'language_iso' => $this->context->language->iso_code,
'logo' => $this->context->link->getMediaLink(_PS_IMG_ . Configuration::get('PS_LOGO')),
);
}
public function initContent()
{
parent::initContent();
$this->context->smarty->assign($this->getSmartyVariables());
header("Content-Type:text/xml; charset=utf-8");
$this->setTemplate('module:ps_feeder/views/template/front/rss.tpl');
}
}