As you get started with your return, TurboTax will ask you some general questions about what may have changed financially in the last year. You may have answered a question about rolling over a 401k. If so, typically that means that you should have received a Form 1099-R to enter as part of your return and report the rollover.
Financial institutions have until January 31st to either mail you a Form 1099-R or give you access to the form online. You might want to wait a little longer to file your return because your Form 1099-R may be coming that should be included.