If you have not yet been notified if your return was accepted or rejected you will need to wait to see if your taxes have been accepted or rejected.
If rejected, you will simply need to fix whatever error caused it to be rejected, then add in your 1099-INT and then resubmit your return.
If accepted, once your return is processed you will need to follow these instructions to Amend Your Return once the 1040X is available in Turbo Tax. You will see your refund/amount due set back to $0, you will then be able to add your 1099-INT.
Your amended return must be paper filed. When you get to the end, it may "appear" that you can e-file it, but it must be mailed. It will take 10-14 weeks for the IRS to process your amended return. Once submitted you can check the status of your amended return here Where's My Amended Return
The amended forms are not available quite yet in TurboTax. They are expected to be available in early to Mid-February.