Tds on arrears of salary

TDS would be deducted, no relief in that.

But assessee can get tax relief of arrears by filing Form 10E to income tax e-filing site along with ITR to get the refund of any excess amount.

If an assesse has received arrears of Salary on 28.12.2019 for FY 2016-17 to 2018-19, can he file form 10E before completion of FY 2019-20 or it can be filled only after 31.03.20?
Sir, is it practically possible to submit copy of submitted form 10E (or if it can't be submitted then Computation sheet) to employer for lower deduction of tds on arrears of Salary?
Please Guide..