You should have entered this in Deductions & Credits in 2015 TurboTax. The Roth conversion gets reported on your 2016 tax return by entering the Form 1099-R under Wages & Income -> Retirement Plans and Social Security -> IRA, 401(k), Pension Plan Withdrawals (1099-R). The basis that transfers from line 14 of your 2015 Form 8606 to line 2 of your 2016 Form 8606 will be used in calculating the taxable amount of your Roth conversion.
If you did not report the nondeductible contribution with your 2015 tax return, you must prepare an file the 2015 Form 8606. This can be done by amending your 2015 tax return.
