Hi,

Try the following steps.

Step 1 : Go to the Inventory module.

Step 2 : Click on "Products" to view a list of all
products in your inventory.

Step 3 : Locate the product you want to add stock to and click on
it to open the product form.

Step 4 : Click on the Update Quantity Button inside Product
Form.

Step 5 : Click on the Create Button and Update the Counted
Quantity and Apply.

Step 6: Go Back to the Product Form you will see the Stock is
Updated.

Regards