Hello Robson,
The Batch determination will depends on the Batch entry which will define in the material master MRP2 View
if the production order quantity has been increased / Decreased in that situation you have to assign the batch number through the batch determination as suggested by Brahmankar
So please select that line item and make the batch search procedure
against that quantity you can be able to select the batch number as per the FIFO process
Regards,
Venkatesh..