To adjust the averaged unit cost (for one or more products) the process is this:
Click INVENTORY > New Adjustment. Follow the instructions on screen to download the XLS file. Save the file in your computer and keep a copy of it
For only the products you want to update the unit cost for, set the stock to 0. You can remove the rows of the "good" products from the spreadsheet
Save the file as CSV or Unicode TXT and upload this new version. This will zero the quantity of these products to the selected Inventory Location
Repeat the process: click INVENTORY > New Adjustment. Download the XLS file again. Keep only the products you want to update the unit cost for. Set the correct quantity and the correct unit cost, save as CSV or Unicode TXT and upload this new version
Important: Keep in mind that if you have multiple warehouses, you need to zero the quantity in all your warehouses first. Then, import the correct physical quantity and the correct cost as per the instructions above.
Note: The above assume that the product(s) for which you want to update the unit cost for have non-zero stock. If the stock is zero, then, by design the unit cost is zero. It will be updated with your first bill (Purchase Bill/Receive On Consignment).
Or login to your account.