Reporting a back door Roth is a matter of reporting a non-deductible Traditional IRA contribution and a Form 1099-R for the conversion.
Using TurboTax Online, you will need the Deluxe version or higher. Any version of the CD/downloaded TurboTax will have the required forms.
For your reference, see the information below for step by step instructions to report the back door Roth.
https://ttlc.intuit.com/replies/6768029
[edited 4/5/19 | 8:25 am PST]
