ERP BOM designator not updated

I’m trying to make a BOM for assembly of electornic module using ERP. There are too many components in the BOM excel sheet. So i’m trying to copy them all from excel sheet and paste in ERP BOM. After pasting all data observed that the Designator column doesn’t filled any data as this column use to locate where to place perticular component.
I have arranged the data in excel sheet in format like `Item code - Designator - Qty - Nos’. Still the Designator column gets empty.
Can you please help to solve this problem.
Please find attached image.