Wrong details furnished in itr of a.y 2013-14 and so on

Hello everyone. a person filled ITR-4 from a.y 2010-11 showing rs 800000 as advance given for flat in balance sheet however he continued to show it as such till a.y 2015-16 though he has made full payment for flat long ago (2012-13). Now since the assessment is complete for all these year. how can i rectify this mistakes.additional information.
1) he registered the above flats in 2013-14 for 2100000.
2) he sold the flat in A.Y 2016-17 for 31000000.