I efiled my federal return with Turbotax and was ACCEPTED by IRS on Jan 15, 2019. I forgot to add 2 1099R forms to it. How do I add these to my 2018 return?

Since you have already e-filed and your return has been accepted, you will need to amend your tax return to add your two 1099-R forms.  I am attaching the AMEND instructions.  You have 3 years from the due date to file it and you should wait until your tax return is fully processed and you have your refund before you file the amendment.   https://ttlc.intuit.com/replies/3288565