If ive been incarcerated and missed tax deadline, how do i file for an extension?

[Carl]

You don't and you can't, since the tax filing deadline is already past. You're just late filing is all, and there's nothing you or anyone else can do about it.  There's nothing "special" you need to do to file your tax return now. Just complete it, and file it. Then, if you are due a refund there will be no late penalties assessed. However, if you owe the IRS, then you can expect to be assessed a late filing penalty and a late payment penalty. So the sooner you get this done, the better.