Salary arrears_taxability of Interim relief

Sir I received Interim relief of Rs. 1lac in Dec18 under VII Fin. commission. Balance arrears of Rs.4 lacs received in Oct. 20. For 5 lacs monthwise breakup is given by employer for apportionment benefit of 89(1). Which amount is considered as arrears full 5 lacs or actually received this year i.e. 4 lacs (net of interim). If I take net amount there is no relief u/s 89(1). Further arrears is full 5 lacs to be distributed over last 4 FYs. Hence I consider 5 lacs is correct. But the problem is I have already paid tax on 1 lac in AY 19-20. The excess tax paid on interim cannot be claimed as refund now due to time lapse. What is the solution