To allow TurboTax to
know that you have Roth IRA contribution basis, you need to enter your Roth IRA
contribution under Deductions & Credits. Scroll down to Retirement and Investments and then choose Traditional and Roth IRA Contributions.
This will then allow
TurboTax to apply this contribution basis against your Roth IRA distribution,
resulting in TurboTax calculating on Form 8606 Part III that the taxable amount
of your distribution is zero.