I assume you are referring to a COVID-19 related distributions, not a loan. loans don't go on your tax return.
If you paid back before you filed your 2020 tax return, then that pay back would be entered on your 2020 tax return. Did you do that? If not, you need to amend 2020.
assuming rounding, 13,333 -15,000 is -1,667 which goes to your 2021 tax return so the second taxable part on your Form 8915-F will be 11,666.
If you report you paid back 15,000 before filing your 2021 return, don't amend but you will be off by a year on your 5498 and may be questioned by the IRS.
