You will need an import file that contains the new stock value, price information and the variation SKU. For this process to work correctly, your products will need to have unique SKUs.
- Create an "Existing Items" import to WooCommerce Products: https://d.pr/i/c5daMc
- On Step 3 of the import process, leave the Product Type set to Simple, add the new price information to the General tab (https://d.pr/i/P6XQhC) and the new stock value to the Inventory tab: https://d.pr/i/iN9S5t
- On Step 4 of the import process, select to match on the custom field _sku and add the SKU element from your import file: https://d.pr/i/7EwWTl
- Also on Step 4, select to update the custom fields _price, _regular_price, _sale_price, _stock and _manage_stock only: https://d.pr/i/c1iZm7