Filing of return of individual assessee when the timelimits under section 139 have expired

I have a taxable capital gain for PY 2015-16 and I have failed to file the return.. based on suggestions, the amount has been parked till date in a special capital gains account. I want to withdraw the amount now and pay the capital gains along with interest applicable.. what are the options available to me in this regard? I do not have any other sources of income for any other Py. (fd amount 21 lakhs)