Amendment or credit Note

Dear experts in December month First two items billed to registered dealer like 500000 and 300000 plus tax. After the dealer not received 300000 item the same date he wants to reverse the invoice.so I revised invoice To 500000 and submit to dealer on the same date. At the time of filling I filled older invoice in gstr1 and gstr 3b. Right now what i do in January month return amend the invoice or raise the credit note