You should have received two Forms 1099-R from the broker, one 2015 Form 1099-R for the original conversion and the other either a 2015 or 2016 Form 1099-R for the recharacterization. Enter these exactly as received and answer the follow-up questions as they apply relative to the moment that the distribution was made.
The fact that TurboTax is mentioning splitting a Form 1099-R suggests that that when entering the Form 1099-R for the original conversion you are inappropriately indicating that some portion was rolled over rather than being converted. You should instead be indicating that you converted the entire $X to a Roth IRA, then on the following page indicate that you moved some of this back to a traditional IRA. The next page will ask how much of the original conversion was left in the Roth IRA, that would be 1/3 of $X.
