Change Bom in Production Order, then do MRP ,doesn't work

Hello Gurus:

I am a freshman in PP domain. I am currently trapped in an issue related to MRP

After Production order generated, I manually add two component under the Production order (CO02-> component overview->add new items here). From my understanding, if I do MD41 now, such changement should be considered in the planning. But it is not! when I check the MD21, the lower-level code of the new added component is 999, which identified this component is not considered by MRP run.

Could you please tell me some best pratice for my scenario?(any parameter needed to be set? any indicator missing?)

Is there any link avail for such sceranio( change bom under production order manually, and redo MRP )?

Thank you all!

Br

Alice.