Defective

You can correct the defect. Once a defective notice is not replied you cannot revise as non replying to the defective notice will make your return invalid. All you can do now if you havent replied to defective notice is 1) reply to defecive notice now and also ask for condonation of delay as it is only 5 days or  2) file a return u/s 139 (4) as belated return.

2 ways that can be done. 

1 - File a response u/s 139(9) I.e defective return. Also apply for condonation for delay

2 - File a belated return u/s 139(4)

It is better to file a response to the defective notice and ask for condonation of delay rather than filing belated return because there are chances for AO to treat the original return filed as invalid and if there are any losses in the given fy., then they may not be carried forward as the return filed would be a belated return.

Condonation of delay means pleading before the AO to accept the late filing / delay in filing the defects due to certain valid reasons