You can alter the inventory count for a product and any related variants by updating the product's inventory settings. Here's a breakdown of how to make those changes.
In the dashboard, pick the product whose stock you need to update. If it has different variants, make sure to select the particular variant.
To change the stock, navigate to the Details and then Inventory tab. Pay attention to the amount of stock that has been set aside for current orders.
Save your changes when you are done.