Gstr4 annual return wrong filed 2019-2020

A gst registered composite scheme dealer gstr4 annual return 19-20 wrong filed.

Sales of taxable turnover Rs: 8,54,000/- cgst 4270 and sgst 4270 tax paid shown in composite return cmp-08 filed in 19-20.

 same turnover and same tax paid amount auto populate table 3(1) in gstr4 annual return in 19-20.

But dealer mistake wrong filed table no.6 outward supplies detailes(sales  of taxable turnover) nil mentioned in gstr4 return.

Question:

1.Dealer how to adjustment producure mistake shown in gstr4 annual return 19-20.

2. Mistake amount adjustment in gstr9a annual return or gstr4 annual return 2020-2021 adjustment amount.

3. Composite dealer gstr9a manadatory and last date of filing return in 19-20.