Product linking after Universal Product Import (xml/json)

When importing goods into the box with this action Generic product import (xml/json) We have in the "linking products" on the right side, there are no products to link, but if we remove all products from the box, on the right side of the linking, all the removed products appear. http://joxi.ru/zANLV3Vi6blwpm The question is how to implement product linking when using the action "Universal product import (xml / json)" The situation is that we import 4 different suppliers into the box with this action and different suppliers have the same goods, so we need to link them. Question: How to implement it?