Go to Products → Serial Numbers where you can find the Import Serialnumbers (csv) button. Select your file and click on Import.
The file format needs to be in the following structure:
You can also add multiple numbers for one product:
By default the product title is used as label name, but you can also specify the label yourself:
You can only upload 500 serial numbers in one CSV file.
You can also create a product serial number without a shipment