Contact the issuer of the 1099-R to request a copy of the form be sent to you (best option)
If you have an online account with the issuer (bank, brokerage, etc.) often there is a statement/tax documents section where you can download copies of your tax forms.
Otherwise you may need to call the issuer to request another copy.
Request your Wage and Income transcript from the IRS
One note for this option - often the transcript will not have the tax ID information from the form issuer, which is generally needed for e-filing. You may need to contact the issuer for this information, or if you have a form from a prior year from them, you can get the tax ID there.
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