Mistake 3b

one gst taxpayer who submitted gstr1 every month i.e. 2017-18, 2018-19, 2019-20 till but he doesn't show liability amount i.e column 3.1 in gstr3b he only show input column in his input credit amount. Because he think that gstr1 when submitted that liability amount auto populate in gstr3b. Now what he can do ?