Gst on car repair

Hi my query ( i am a car dealer) is when we sale car from my agency i charge we charge Local tax(CGST nd SGST) whether buyer give its GSTIN(local/ interstate) or not.  as we make manual bill..
Now Problem arise at the time of repair/service as bill was made from company software and it charge on the basis of GSTIN, if same state GSTIN then It charge local tax otherwise IGST.
what to do in the case???  plz help