The payment plan is directly with the IRS and not TurboTax.
The IRS Website has information on how the payment installment program works: https://www.irs.gov/payments/payment-plans-installment-agreements
I also found a contact number, although you will experience long hold times near the tax deadline. "You may also request a payment plan by calling the toll-freenumber on your bill, or if you don't have a bill, call us at 800-829-1040 (individuals) or 800-829-4933 (businesses)."
