No, you do not amend your 2019 for the payments made in 2020 for 2019.
You can't amend returns for prior years to reflect social security benefits received in a single lump-sum in the current year. You must include the taxable part of a lump-sum payment of benefits received in the current year (reported to you on Form SSA-1099, Social Security Benefit Statement) in your current year's income, even if the payment includes benefits for an earlier year.
See Back Payments | Internal Revenue Service.
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