Here's how to correct mistake in your income tax return
If original return has been filed in paper format or manually, then technically it cannot be revised by online mode or electronically.

When a tax payer discovers any mistake or omission of important details or making a wrong statement in the original income tax return submitted, she can rectify the same through e-filing portal of income tax department within prescribed time limit. A revised ITR can be filed at any time during the assessment year or before the assessment made whichever is earlier.
If original return has been filed in paper format or manually, then technically it cannot be revised by online mode or electronically.
A revised ITR means filing a new ITR with corrections under Section 139(5) of the Income Tax Act.
Here is the step-by-step guide to file the Revised ITR online through e-filing portal of the Income Tax department
1) Go to the e-filing portal of income tax department
2) Login to the e-filing portal using your PAN number, password and captcha code and click 'Login'
3) Click on the 'e-File' menu and click 'Income Tax Return' link
4) On the Income Tax Return Page, your PAN number will be auto populated. Select Assessment Year and ITR Form number
5) Next, select 'Filing Type' as ' Original/Revised Return'
6) Select 'Submission Mode' as 'Prepare and Submit Online'
7) In the Online ITR Form under 'General Information' tab, choose the 'Return Filing Section' as 'Revised return under Section 139(5)' and 'Return filing type' as 'Revised'
8) Enter the 'Acknowledgement number' and 'Date of filing' of the original ITR.
9) Fill or correct the relevant details and submit the ITR
10) e-verify the returns