Automatic purchase order creation from purchase RFQ

AX2012 R2.

I need to make a customization on auto creation of purchase order after purchase rfq acceptance.

I have added one field in PurchRFQCaseLine that i want to update when creating the purchase order line.

Can any one guide me which class / method i need to customize to get the following update. I have tried to debug but did not find the clue i would appreciate any help in this regards.

Thanks