Long term capital Gain of Mutual funds

It is mandatory to be declared, provided your gross total income is above basic exemption limit.

Thanks for the information

Sir I have missed this information for the FY 2020 -2021 how can it be rectified

If it is LTCG over equity MF, then it is tax exempt upto the limit of Rs. 1 lakh, thus there will not be any additional tax liability. As such not possible to file updated return, unless there is any additional tax liability.