If I forgot to add a 1099-R to my already submitted taxes, should I do an amendment or wait until next year?

[rjs]

Right now all you can do is wait. The IRS will not start accepting tax returns until January 28. Until then TurboTax will just hold your tax return, but you cannot make any changes. Within a day or two after the 28th you will get an email telling you that your tax return has been either accepted or rejected. If it's rejected you can add the missing 1099-R when you correct the reason for the rejection, and then resubmit the return. If it's accepted you will have to wait until the IRS processes it and you get your refund. Then you can file an amended return (Form 1040X) to add the 1099-R.

You cannot wait until next year. A 1099-R for 2018 has to be included in your 2018 tax return.