Thank you for the questions as I dug out a more clear picture of the past.  I was asked to amend a 1040 to include the interest expense  for the amount the individual paid on the loan to buyout his partner.  I was told the buyout was in 2016.  2 guys made a S-Corp and a K1 was issued/received in 2015-2019. 

(On the S-Corp return in the tax software is a K-1 (1065) form.  The prior preparer might have had this in the file by accident or something, don't know why.  I should not have listed anything about this in my question.)

The old partner is listing the self financed loan interest income on his tax return, so he wants to include the expense on his return.  He has never claimed this expense before.  I just took over this practice and the returns were done in ATX software.  I am moving over to ProSeries for 2020.  I thought I would amend in ATX instead of doing the return from scratch (entering & amending) in ProSeries. 

I was thinking to enter on 1040 Schedule 1, part I additional income, line 8 as negative income.