The first step is to be kind about it. Send a message over YouTube explaining that you are the developer and kindly ask them to take it down. It is important to be very polite and non aggressive about it.

You can also report the video stating it is advertising illegal activity.

As others have posted, this guy has no subs, and not every view/sub equates to a purchase or instance of pirating. You may lose a few potential sales, but you need to understand this is not lost revenue as there was no guarantee they were going to buy it in the first place, and you have not lost something of limited stock.