I need to update Department Value on Item Fulfillment , How can this be achieved?

Map/Reduce depending how many you need to update. Note if they are in closed periods you might not be able to update them.

I have around 2000 records to update. and it is on closed period. Thank you.

There is an accounting setting to allow updating non_GL fields on transactions that are closed, so you might be able to update them if you turn that on.

Thank you so much.