Dear ,
there are two possible way:
1 ) you can try to execute a confirm with scrap quantity, so that the following operations update the production quantity to 6 pc.
2) If you need to have the stock scarp quantity for quality activity or other check you have to execute a issue good moviment with 101 type moviment (only this moviment decrease the order quantity and not 531 type moviment.
I hope have been useful for you
Daniele