When you put in the 1099-R in the interview steps there should be questions about how much was for a rollover to a Roth, which should flow through to the 8606 in Part 1 Line 8, and/or Part 2 Line 16. You can see this on the 1099-R in Forms view if you scroll further down to "additional distribution information'.
On the 8606, Part 1 is used to track your basis in your IRA(s) if you made non-deductible contributions (and carry it over from year to year in Turbotax). If you do have a basis it calculates the proportion of your Roth conversion that is taxable and your remaining basis to carry forward, and this flows into Part 2 to calculate the final taxable amount in Line 18.
At some point you'll get a Form 5498 for the Roth that will confirm the rollover amount but you don't need that for filing (you may get one now, and/or in May since the deadline for Roth conversions is April 15).
