Reply to demand notice after due date

One of our clients filed a return for AY 2018-19 himself, without claiming chapter VI deductions. He later received a notice under section143(1)(a) in January demanding Rs. 57,000, which he ignores. Now after 31st March 2019, he contacted us for solution of this.

In my view, we cannot revise the return, neither we can reply online through E-Proceeding, nor we can go for rectification u/s 154, as he forgot to claim deduction in original return.

Please suggest a solution for this situation.

Thanks in Advance.