Hi there, @craig-ad.
You can enter an stock quantity adjustment without recording a purchase or sale so it'll not mess up your expenses. Let me walk you through the steps.
Here's an article you can read for more details: Adjust stock quantity on hand in QuickBooks Online.
You might also want to check out this article to know the impacts of stock tracking on balance sheet and profit & loss reports: Impacts of stock tracking on balance sheet and profit & loss reports.
Please keep in touch if there's anything else I can do to help you succeed with QuickBooks. I've got your back. Have a great day!