How to avail benifit of output vat liability before 1 july and after 1 july with gst credit.

If i am a trader and before gst implementation my product liable for 9% vat liability and after gst implementation product liable for 5% gst, so how i adjust my vat liability or input tax credit against gst and excess (9-5) =4% liability occur on trader which will waive or borne by the buyer....so please suggest me with proper guidelines..
Thanking You..