Since you have already e-filed or mailed the return, you will need to wait until the IRS has accepted it. Once they accept it and you have received your refund, then you can amend it to add the 1099-R. If it gets rejected, you can just make the needed changes and file again.
After you have received your refund, you can go here and get instructions https://ttlc.intuit.com/questions/3061514 for amending that return. At the time of doing the amended return, it will show if you will get another refund or if you owe anything at that point. If you owe, just mail it in with the amended return once you have completed it.
Once you are ready to amend, you can find steps here for how to enter the 1099-R https://ttlc.intuit.com/questions/2562810
NOTE: You will have to print and mail your amended return because an amended return can't be e-filed. It takes the IRS around 16 weeks to process your amended taxes.