Deductions & credits

To apply your federal refund to next year, enter it under

Federal Taxes Tab or Personal (Home & Business)

Other Tax Situations

Additional Tax Payments

Apply Refund to Next Year - Click the Start or Update button

 

To apply your state refund to next year, enter it under

State Taxes tab

And keep continuing and stepping though the interview about a dozen or more screens and it will finally ask how much you want to apply.  It is probably one of the last questions in the state section.