PHP - Bitrix (Clear fields, get list since infoBlock and set field name want clear)

clear_fields.php

CModule::IncludeModule("iblock");
$ob=CIblockElement::GetList(
array(), 
array("IBLOCK_ID"=>62, "PROPERTY_PORTAL" =>885), 
false, 
false, 
array("ID","PROPERTY_LAST_EXECUTION"));

while ($res = $ob->GetNextElement()) {
 $arFields = $res->GetFields();
 $arFields['PROPERTIES'] = $res->GetProperties(); 
//----------------------------------------------
//SET ANY DATE
//$properties["LAST_EXECUTION"] = "07/25/2017"; 
//----------------------------------------------
//SET CURRENT LAST_EXECUTION AND LESS NUMBER DAY
$properties["LAST_EXECUTION"] = date("m/d/Y",strtotime("-5 day",strtotime($arFields["PROPERTY_LAST_EXECUTION_VALUE"]))); //SET -5 DAY FOR PAYSPAN
//----------------------------------------------
//SET EMPTY FOR CLEAR FIELD
//$properties["LAST_EXECUTION"] = ""
//----------------------------------------------
CIBlockElement::SetPropertyValuesEx($arFields['ID'], false, $properties);
//----------------------------------------------
//VIEW FIELD LAST_EXECUTION
//echo ($arFields["PROPERTY_LAST_EXECUTION_VALUE"])."\n";
//----------------------------------------------
//VIEW ARRAY PROPERTIES ("ID","PROPERTY_LAST_EXECUTION",ETC)
var_dump($properties)."\n";
}