Using the "Import Inventory" area will allow you to update your QOH (Quantity On Hand).

You can export your Current QOH levels in the "products" area of your ECommerce Module.

See screenshot:

Once you export your current inventory level, you can update the file to reflect the updated QOH.

This is what the exported (or newly created file if creating one from scratch) will look like:

Now that your inventory CSV is updated you can now import it.  You will need to go to the "Import Inventory" area of your ECommerce Module.

Click on "browse" to locate your updated inventory file, and click open.  Once you see your file listed next to the "Browse" button you can click "import".

And you are done.

Please feel free to contact support if you have any questions.