Hello Kiran,
There are two component in this scenario,
- Cost Rejected Material : This is the cost of SFG which got rejected in FG processing so this material you can reject this material by standard SAP scrap movement or by creating separate production order for scrap code. If you go with scarp order the you can book the cost on FG order as settlement receiver.
- Cost of FG process: When SFG got rejected there might be some processing done on SFG. This cost you can directly book through CO11n on that FG order as normal routing or process cost.
Regards,
Shekhar