I created a custom record to store multiple external systems' IDs per vendor (fields are ID, vendor and the external system). Then, I created a custom entity field (multiple select) to store those custom record instances in the related Vendor record. When I try to create the custom record from the multiple select entity field, it's automatically selected or "linked" to the Vendor record. However, when I import the custom records, they are not selected or "linked" through the multiple select entity field. How can I make sure that the custom records are selected in the multiple select entity field?