Hey there @itsmeifti ,
The Shopify Admin’s built-in inventory import tool requires additional columns such as the Handle and Options columns, unfortunately.
If you’re open to using an app, our EZ Inventory app is designed specifically for updating the available quantity of existing products/variants in Shopify. You can update the stock levels in Shopify using a CSV file that only contains a “SKU” and “Stock levels” column.
You can do a manual upload of the CSV file or automate the updates as well if the CSV file can be downloaded from an FTP/SFTP server or a public website URL (such as a Google Drive shared link).
Feel free to contact us in case you have any questions about the app.