How to repay the deferred Self-Emloyment tax under CARES

On my 2020 return I elected to defer part of my SEP tax as provided by CARES. I know that I need to repay half of the deferred amount by December 2021 and the other half December 2022. My question is there a special voucher to accompany my check? If I just send a "stray" check in December how will IRS know this is my deferred SEP rather than say an estimated tax payment?

Thanks

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