Mistake in gstr-1

Mr. A will amend the details in next GSTR 1...

How will you amend the details?.Here C will reject A's return.Shall we amend the correct GSTN in that stage itself?? or Does A again needs to file his return in Next month with correct GSTN number.(If Tax applicable A don't want to pay tax again since he paid tax his earlier return only by mistake he plunged wrong GSTN number) which way we should go?