What are you trying to do? The filing deadline for 2020 tax returns was May 17, 2021. It is too late to submit estimated tax payments for 2020. The tax owed for 2020 was supposed to be paid by that deadline.
Or do you mean you made the 2020 estimated payments by some other method and you just want to know what to do with the paper vouchers?
Please explain why you are asking about 2020 ES vouchers at this time.