CDavExchangeCalendar::Update

public function Update($id, $arFields, $params = null)
	{
		$this->ClearErrors();

		$request = $this->CreateSOAPRequest("POST", $this->GetPath());
		$request->AddHeader("Content-Type", "text/xml; charset=utf-8");
		$request->AddHeader("SOAPAction", "http://schemas.microsoft.com/exchange/services/2006/messages/UpdateItem");
		$request->AddHeader("Connection", "Keep-Alive");

//			if ($params['editInstance'])
//			{
//				$id['XML_ID'] = $params['instanceExchangeId'];
//				$id['MODIFICATION_LABEL'] = $params['changeKey'];
//			}

		$arFieldsNew = $this->FormatFieldsArray($arFields);
		$request->CreateUpdateItemBody($id, $arFieldsNew);

		$this->Connect();
		$response = $this->Send($request);

		$this->Disconnect();

		if (is_null($response))
		{
			return null;
		}

		if ($this->ParseError($response))
		{
			return null;
		}

		$arResultItemsList = [];
		$xmlDoc = $response->GetBodyXml();

		$arResponseMessage = $xmlDoc->GetPath("/Envelope/Body/UpdateItemResponse/ResponseMessages/UpdateItemResponseMessage");
		foreach ($arResponseMessage as $responseMessage)
		{
			$arResponseCode = $responseMessage->GetPath("/UpdateItemResponseMessage/ResponseCode");
			$responseCode = null;
			if (!empty($arResponseCode))
			{
				$responseCode = $arResponseCode[0]->GetContent();
			}

			$responseClass = $responseMessage->GetAttribute("ResponseClass");

			if (
				(!is_null($responseClass) && ($responseClass !== "Success"))
				|| (!is_null($responseCode) && ($responseCode !== "NoError"))
			)
			{
				$arMessageText = $responseMessage->GetPath("/UpdateItemResponseMessage/MessageText");
				$messageText = "Error";
				if (!empty($arMessageText))
				{
					$messageText = $arMessageText[0]->GetContent();
				}

				$this->AddError(!is_null($responseCode) ? $this->Encode($responseCode) : $this->Encode($responseClass), $this->Encode($messageText));
				continue;
			}

			$arCalendarItem = $responseMessage->GetPath("/UpdateItemResponseMessage/Items/CalendarItem");
			foreach ($arCalendarItem as $calendarItem)
			{
				$arResultItemsList[] = $this->ConvertCalendarToArray($calendarItem);
			}
		}

		return $arResultItemsList;
	}