Route and Order enhancements

Hi ,

I have a scenario , where PO is creating a SO and depending on Plants(Updated in the text tab of SO ) the route is getting updated in the Sales Order (Screenshot). Now if the Plant is D764 , the route is SGINOA . Now this route is getting populated via some exits . How do I check the same , how its getting updated/ or the background code of it  ?

Thanks

MM_sD