Please read
the TurboTax FAQ for more information on "Can I file a Form 9465 (Installment Agreement Request) in TurboTax?":
Can I file a Form 9465 (Installment
Agreement Request) in TurboTax?
If you already filed, or you're unable to find this option in TurboTax,
you can apply for a payment plan at the IRS Payment Plans and Installment Agreements web
page (make sure you've filed your return before applying through their site).
