If you have already printed your return, and the system thinks you are complete, you can "trick" the system into re-opening it. Choose the option to add a state. You will not actually add a state, but you will get back into the software to continue working on it.
Now, follow the usual path to add the 1099-R: Federal > Wages & Income > IRA, 401(k), Pension Plan Withdrawals (1099-R) Add/Edit
TurboTax Expert Assist
Get answers to all your tax questions
Our experts are available on-demand, no appointment needed. Get help all year long with TurboTax Expert Assist.