1.create one non val material for Operation to be processed outside.
2.Put this material in BOM of FG with -ve and +ve Qty.
3.Assign this quantities in routing for 2nd and 3rd operation, so in PR this component will come automatically.
4.COnvert PR to PO for that vendor.
5.Send this assigned component to vendor MB1B-541
6.DO MIGO (movement 101 and 543 will be triggered.)
7.Confirm 3rd operation after MIGO of 2nd operation.
Hope it explains..