You have to file an amendment but wait until your tax return is fully processed and you receive your refund or your balance due is deducted from your account. When you do your amendment to add your 1099-R, TurboTax will calculate your new refund or balance due based on your additional income. If your original refund was more than what you should have received when your 1099-R is added, you will have a balance due.
For more information and instructions, review the TurboTax articles How to Correct Federal Tax Returns, How to File an Amended Tax Return with the IRS and Video: How to Amend Your Tax Return.