You'll use 2017 TurboTax to amend your 2017 tax return. Since you appear to be using the CD/download version of TurboTax, make a copy of your originally filed tax file and then begin the amendment using this tax file. You'll need to revisit Personal Income -> Retirement Plans and Social Security -> IRA, 401(k), Pension Plan Withdrawals (1099-R), edit the original Form 1099-R reporting the Roth conversion and in the follow-up to that entry indicate the amount of the original conversion that you recharacterized. TurboTax should prompt for an explanation statement where you'll again indicate the amount recharacterized and the adjusted amount transferred back to the traditional IRA (from box 1 of the code R 2018 Form 1099-R. You can enter the code R 2018 Form 1099-R into 2017 TurboTax, but 2017 TurboTax will essentially ignore it.
To amend your 2017 tax return:
https://ttlc.intuit.com/replies/3288565
