Hi there, @Suf.

Thank you for joining us here in the Community. It would be my pleasure to help you with how to rectify the stock shrinkage in QuickBooks Online. 

All you need to do is delete the products in the stock shrinkage report to decrease the stock. Let me guide you how:

1. Go to the Accounting tab located on the upper left side. 
2. In the search box, type Stock Shrinkage then click Run report. 
3. Locate the duplicate and hit the date.
4. Hit More, then tap Delete. 

To learn more about how to modify products and services in QuickBooks Online, please visit this article for future reference: Remove or merge a product or service.

Let me know if you need anything else moving forward. I'm always here to help. Take good care always,