Reservation SO - Prod.Order - PO

experts, can anybody help me to understand how to deal with reservation. i have production orders open, and i want to several POs to supplier open. how i can set the component in prod.order line component to reserve from certain PO. the purpose is to set the reservation on my decision, not by system decision. thank you.

from the production order, press line==>components, then functions reserve, then choose the po’s to reserve from