If any error is discovered after the return has been filed then such return can be revised u/s 139(5). Revised Return of Income Tax can be filed by an assessee any time before the end of the relevant assessment year or before the completion of the assessment, whichever is earlier.
An assessee can revise his returns at any time before the end of the applicable assessment year (for e.g. 31st March 2019 for assessment year 2018-19) or before the conclusion of assessment by the Income tax department. (whichever is earlier). (Read More: Revision of ITR)