You can pay your deferred self-employment tax amount due on or before December 31, 2021 on the IRS.gov site: How to repay the deferred taxes .
As it appears that your self-employment income was reported on a Schedule C, meaning that you are a sole-proprietor LLC, as opposed to an S-Corp or multi-member partnership, you should select "1040 US Individual Income Tax Returns" and designate the payment as "deferred Social Security tax."
You should register under the primary name on your tax return, which is the first name (yours or your spouse's).
Please be sure to apply the payment to the 2020 tax year where you deferred the payment. Finally, if you are using Direct Pay, select the reason for payment, "balance due." If you are using the "Card Program" to pay with a debit or credit card, select "installment agreement" as reason for payment.
