If a person after furnishing the return finds any mistake, omission or any wrong statement, then return should be revised within prescribed time limit.
A return can be revised before the end of the Assessment Year or before the completion of the assessment; whichever is earlier.(w.e.f A.Y 2018-19)
However for the earlier Assessment Years preceding to the Assessment Year 2018-19 , a return can be revised before the expiry of one year from the end of the Assessment Year or before the completion of the assessment by the Department; whichever is earlier. (till A.Y 2017-18).
If original return has filed in paper format or manually, then technically it cannot be revised by online mode or electronically.
Revised return can be filed online under Section 139(5).