Supplier items that are created without being assigned to a master item can be subsequently linked to master items in the supplier's range list.

1. Go to the  Supplier account and click on  Purchasing >  Range. A list of existing supplier items will open.
2. Open a  Supplier item.
3. In the top line next to the (empty) item name, click on the expand triangle and assign a master item by clicking   New,  Search or  Recently opened records.
4.  Save and close.