Once you submit and verify your income tax returns, an income tax Assessing Officer will authenticate the data you have entered and will send you an "Intimation u/s 143(1)" of the Income Tax Act. Here, you will need to match the data you’ve submitted and computed u/s 143(1) by the assessing officer. If there is a mistake, it will need to be corrected by submitting a rectification request by you..
You can submit a rectification request after the income tax return is processed or on receiving an Intimation u/s 143(1). You can rectify mistakes apparent from the record. Under this section, one can rectify clerical, arithmetical mistakes, a mismatch in tax payments, inclusion of income chargeable under an incorrect heading, and even changes in your resident status, Rebate not allowed, TDS Credit in 26AS but not allowed by officer. Further, there must be confirmation that the mistake is apparent from the records and it is not a mistake that requires debate, elaboration, investigation, etc.
You can file a rectification request within 4 years from the date of the order that needs to be rectified, not necessary the original order. Thus, even after you file a rectification request and there continues to be an error in the revised order, you can file another rectification within 4 years from the date of the revised order.
If you unintentionally failed to include certain income or forgot to claim additional income exemptions, then file a revised return. There is a possibility where one could have forgotten to include interest income or even misplaced a donation receipt to claim exemption under Section 80G. Means there is a change in income or Deduction or claim we can file revised return. A revised return can be filed even before receiving an Intimation u/s 143(1).
You can file a revised return under Section 139(5) of the Income Tax Act "any number of time" before the end of the assessment year.