Quantity can be adjusted via a bulk file and you can add or subtract any amount to the inventory of your products.
To do this, you need to create a spreadsheet with two columns, which are productdata.sku and qty_adjust - as below screenshot.
If the amount is negative, it will subtract this amount from your current inventory quantity.
If the amount is positive, it will add it to your current inventory quantity.
Once the bulk file has been prepared, all you need to do is upload it into the StoreAutomator, and it will automatically adjust your quantity.