It is no longer possible to e-File form 1040-X for prior years.
You mailed away your 1099-R which you would need to attach to your 2019 1040-X to get the overpayment back.
If possible, get another copy from your custodian website and print it. Or use the State copy.
Based on what you said, 2020 is not involved; a 2020 1040-X won't help you. Sending that would just make more of a mess.
See IRS web-site to log in and "View your account" and find out what amounts IRS has credited to your 2019 tax return.
