Revised ITR issue

Yes.You can revise the ITR .

You may use ITR acknowledgement number & date of filing original ITR to revise the ITR for AY-2020-21

Yes, You can file Revised ITR for A.Y 2020-21, if there is any mistake in original ITR, which you want to rectify.

From the Assessment year 2017-18, if any person having furnished a return under section 139(1)/(4), discovers any omission or any wrong statement therein, he may furnish a revised return. From the Assessment year 2017-18, even a belated return submitted under section 139(4) can be revised. The process of revise return is specifies under section 139(5).