Once you hit the submit button the return is send to the IRS and state and you won't able to stop it. You will have to wait and see the tax returns gets accepted or rejected. If they get rejected then you can just add the 1099-R.
If the returns have been accepted then you will have to file an amended return (1040X) to make changes. But you might want to wait until your refund or payment is processed. The IRS will only accept amended returns via mail.
Please see the following information on how to amend your return: