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.
And the steps for adding that 1099-R to your amended return are as follows:
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.
And the steps for adding that 1099-R to your amended return are as follows: