Using a Linking Sheet will allow you to bulk attach Digital Assets to Products.
...
Select "Import Products" and click continue.
Upload the spreadsheet you previously created and click continue.
Verify that your data in the Header Attributes matches the data in the Mapped Attributes and continue
This is the validation step. Any error will be listed here. You can also download a full and an error only report to help determine the reason for any errors. Once verification is complete click continue.
Success