How do I amend my accepted tax return? I need to add 2 1099-R distributions.

WAIT for the IRS to process your return, and then amend.   Amending too soon can cause confusion and delays.

Yes, as xmasbaby0 mentioned wait until the original return has been processed. 

If your return has been accepted by the IRS, then you have to file an amended return (1040X) to make changes. But please wait until your refund or payment is processed. Please be aware that you can e-file your 2021 amended federal tax return, but most states require amendments to be printed and filed by mail. Please see How to amend a tax return for instructions.