Purchase requistion Reversal after sourcing in Srm7.0

we r using SRM7.0+Bidding +Classic Scenario

We have CPPR scenario also

by mistake causes Purchase Requistion is converted to Sourcing in SRM.after convertion to Rfx they need to reversal.Need to delete Sourcing &Central system for that PR

How will it possible?

what tables do i need to change regarding this??