Item update child table >> Item Tax

I have a list of items already present in my database, I am using V13. I want to insert a second line for the item tax template on all items. When I try to import data using “Type > Update”, the system keeps overriding the only line of item tax that is already present. Howeverm then I thought I should try “Type > Insert” and then try to upload the same sheet, now it wants to create a new item and starts giving validations for all mandatory fields for item import.

How do I import 2 lines (create one and edit one) while updating the items and not importing new ones?