GSTR3B Return

I wanted to clarify one doubt.

We are the service providers doing Manpower Recruitment Agency with SAC dode 998511. We had raised one invoice to our one of the unregistered client ( local supply) on Sep 2018.  He paid 35% of the amount of the bill as part payment on Oct-19. Now he is saying that he will not pay the balance amount of the bill. Sir in this situation for finalizing our accounts shall we raise a credit note on 31.03.19 to him and take back the  proportionate amount of GST paid by us and adjust  in our Mar-19 – GSTR 3B ( by paying less) and show that credit note in our GSTR 1 of last quarter ( Jan to Mar-19). Pls clarify.

Yes, you can do Mr. Ashok.

Thanks Mr.Chandra Prakesh for your reply