Hello David Soens,
1. If you want to update same quantity for products, please go to Products Manager section at back-end side, select the products on the list then click on Batch button on the toolbar, you can set the quantity for them.
2. If you want to update the different quantity for different products, then you can go to export the products data into Excel file first, then edit Excel file (just with 2 fields: product_sku and product_quantity) and use EShop Import Pro component to import data back to EShop to update product quantity.
Sincerely, Giang
