Hello there, Dave.
Once you create an invoice, your inventory will be reduced according to the quantity that you've used in the sales transaction. These two are directly proportional to each other.
To successfully track inventory and know more about how QuickBooks handles inventory assets, please check out this article: Understand inventory assets and cost of goods sold tracking.
I'd also suggest reaching out to your accountant so you'll be guided further on what other options to record free gifts.
Don't hesitate to leave a comment below if you have any other questions. We're always here to help.