If your Finqu subscription includes the Inventory management feature, you can use the Replenishment feature to add new units to the stock.
Go to Inventory from the left menu.
Click Replenishment.
Search and open the product.
Fill in the quantity, and click Add (or press enter).
After you have made the first replenishment, you can either:
go back to the product list by clicking the Replenishment link at the top of the page or
find the next product with the search function.