Update purchase requisition quantity for external operation

Hi experts,

Is there any way that system will update purchase requisition quantity according to the confirmation of last operation?

For example

If we have an production order with 300 pieces has two operations (1) Internal operation  (2) external operation

If first operation confirmation is 200 or 400, could the purchase requisition bring out the quantity with 200 or 400.

I always get the purchase requisition quantity equal to order quantity which is not reasonable.