Adjustment not reported sale turnover in gstr-4. 19-20

Acomposite scheme dealer sales turnover declare Rs:15 lacs and tax paid Rs:15,000/-  show in cmp-08 return filed in f.y.19-20.if a dealer mistake cmp-08 declare sales turnover not reported table 6  show in f.y.19-20 gstr4  annual return.dealer recently gstr4 f.y.20-21 options opened table 8  cgst 7500 sgst 7500  negative liablity show .

Question:

Dealer mistake cmp-08 declare sales turnover not reported table 6 in f.y.19-20 adjustment next year gstr4 f.y.20-21 (two years 19-20 and 20-21) table 6 show is correct method or not correct in gst act.