If the entire distribution from the qualified retirement plan was rolled over to the Roth IRA, simply enter the Form 1099-R reporting this distribution. The Form 1099-R should show the taxable amount in box 2a and the nontaxable amount in box 5. If you insead split the rollover with the after-tax portion going to a Roth IRA and the nontaxable portion going to a traditional IRA, you'll need to split the Form 1099-R into two for entry into TurboTax, one for each portion.
