Are you asking how to pay the deferral for 2020 SE tax on the 2021 return ?  

no, it has been paid - where is that reflected on the 1040 as an offset to the deferred amounts?

I haven't even looked at 2021 Form 1040 but I wouldn't think it would be on there....unless there will be some special schedule to reconcile amount deferred to amount paid.

I'm just throwing out the possibility that IRS will have an option to apply 2021 refund to the deferred balance.   No different than First Time Homebuyer Credit repayment.

It is a tax for 2020, and payments are due by December 31st.  Why would it show up on a 2021 tax return that has payments due on April 15th (or later)?

I didn't have any clients that deferred but I thought it was 50% 12/2021 and 50% 12/2022. 

My thinking is that (1) you 'deferred' the tax on the tax year 2020 Form 1040 - (2) the IRS is sending notices that 50% (or more) must be paid by December 31, 2021, (3) to close the 'loop' you'll reflect that you deferred the tax - paid the tax - offset the tax.  Ok, I'll stay tuned.

Didn't have any clients that utilize this either... Really what good is it?... Creates nothing but a future issue or work, in my opinion it should have never been offered..