The cost basis of the property was the FMV on the date the person you inherited it from passed. If you sold it for that value or less, and you did *NOT* receive a 1099-S reporting proceeds from the sale, then you have no need or requirement to report the sale on your tax return.
If you did receive a 1099-S, then reporting the sale on your tax return is required.Assuming you closed on the sale in 2020 and did not report the sale on your originally filed 2020 tax return, how you amend depends.
If you used the online version just log into your online account and select the option to amend *before* you open the actual 2020 tax return.
If you used the CD version then fire up the program and click the Amend button, *before* you open your 2020 tax return.