How to bulk edit Magento 2 product attributes
If you want to edit attribute values of a product you need the attribute code of the corresponding attribute. You can find that attribute code in the Magento 2 admin area at the path: Stores -> Product (Attributes). After opening this view, you see the list of all attributes. One column contains the attribute code.
The attribute code should be inserted in the header row of the spreadsheet. If the attribute already exists for while you can find the attribute code in the drop down of the header. When it is a new attribute you have to insert it manually.
After inserting the attribute code you have wait for the next import. The next import will create also the drop down for the attribute values. But if you know already the possible values it is possible to insert them already. You can find them also in the Magento System.