TurboTax's wording where it asks for the contributions to the Roth IRA are oversimplified. Your contribution basis in the Roth 401(k) indeed becomes contribution basis in the Roth IRA when the Roth 401(k) is rolled over to a Roth IRA, so where TurboTax askes for the amount contributed to the Roth IRA, include the contribution basis rolled over from the Roth 401(k). If you entered a code-H Form 1099-R into TurboTax and that Form 1099-R included in box 5 your Roth 401(k) contribution basis, TurboTax would automatically include the box-5 amount in your Roth IRA contribution basis.
