Tax Relief U/S 89

Good evening Sir ? Madam ,

I filed return for the FY 2020-21 for one of my client on 28-12-2021 and received Intimation Dated: 12-05-2022 after 5 1/2 months after revised return filing due date exceeded. In the notice informing the Calculation done u/s 143 (1). But i mentioned gratuity received from the previous employer for the same F.Y. approx. 2 lacs not considered in their calculation and refund paid very low Rs. 30,000/- in place of 2,19,920/-. and un knowingly Iam not submitted Form 10 E before filing return and after return filed to get relief. Based on this, i have some queries plese suggest: 1) May I file revise return now for the FY 2021-2 2) How to get refund the gratuity amount 3) How to sumbit form 10 E for tax exeption for gratuity received / Tax relief U/S 89.