Where by reason of any portion of an assessee’s salary being paid in arrears or in advance or by reason of his having received in any one financial year, salary for more than twelve months or a payment of profit in lieu of salary under section 17(3), his income is assessed at a rate higher than that at which it would otherwise have been assessed, he can claim relief called relief u/s 89(1).

Received arrears of salary, you can claim relief u/s 89(1) from your increased tax liability. You need to file form 10E.

Refer our guide to know the procedure: https://cleartax.in/s/get-help-with-salary-arrears