Setting value on $vCard->Properties(1)

Hi,

I am trying to set QryGroup1 ($vCard->Properties(1)). Reading the value works but how do I write new values (PHP)?

$vCard = $sapCom->GetBusinessObject(2);

$vCard->GetByKey($customernr);

echo $vCard->Properties(1);

DI-Server Docs specify this as read/write-property but this is a function so there is no write access.