how to file sec 119(2)(b)

good evening respected members,
I forgot to e verify my return for ay 15-16, I filled presumptive income my tax refund was 100000, cpc informed me my return was invalid
now I want to file my return under sec 119(2)(b)
please tell how to file my return under this section? or is there any way to back my refund?

thank you.