question

>>> I want to get ItemInstanceId from args and find it in the inventory. Is there an example of cloud script?

Do you mean you want to update items’ custom data using Server API UpdateUserInventoryItemCustomData? If so, you can refer to the following example.

handlers.UpgradeUserInventoryItem = function (args, context) {
    var userItemInstanceId = args.userItemInstanceId;
    var result = server.UpdateUserInventoryItemCustomData
        ({
            PlayFabId: currentPlayerId,
            ItemInstanceId:userItemInstanceId,
            Data: {
                Equipped: "True",
                Slot: "Head"
            }
        });
}

>>> I have to modify and save the cloud script, and then change it to live. Is there any way to test it without live?

Currently, PlayFab doesn’t support testing the CloudScript revision without live, you can only test the CloudScript revision after deploying it.