Simply report the 2018 Form 1099-R on your 2018 tax return and in 2018 TurboTax indicate that you moved the money to another retirement account and the amount rolled over. As long as the rollover was completed within 60 days, the fact that the rollover was not completed until early 2019 is irrelevant. The IRS is knowledgeable of the fact that the Form 5498 showing receipt by an IRA of a rollover contribution might be the Form 5498 for the year following the year of the distribution because of such circumstances.
