How to amend 2020 return that was done using IRS Free File Program delivered by TurboTax?

I need to amend my 2020 return to reflect unreported income.

 

How to amend 2020 return that was done using IRS Free File Program delivered by TurboTax?

 

When I try to amend it online, it says amending it is not supported by IRS Free File Program delivered by TurboTax. I can download the tax file but what software should I use to amend my 2020 federal & state tax return?

 

Please help.