Forgot to claim social security benefits and already filed returns

If the IRS rejects your E-Filed income tax return, you could change your return.

If the IRS Accepts your income tax return, use the amend feature in TurboTax:

If you enter your social security benefits and it does not change your refund or amount due, you do not have to file an amended income tax return. Keep the social security forms for your records. 

If you enter your social security benefits and it does change your refund or amount due, you will have to amend your income tax returns. Wait for the IRS to process your original income tax return before you amend it.  If you are expecting a refund, check for the status at  Where's My Refund? - It's Quick, Easy and Secure. - IRS.gov

The IRS 2016 Amended tax forms will not be ready until some time in February. 

See How to Amend (Change or Correct) a Return You Already Filed to amend your income tax return. Please keep checking the TurboTax FAQ for the status of amended return tax forms.