Can't get TurboTax Desktop 2021 to amend return for third economic impact payments. Option appears under "Federal review" but when I load return (to amend) it disappears.

I'm using TurboTax Desktop 2021 for mac, because when using the account online (free edition) it tells me I need to use the desktop application. When I did this for the first and second payments (which uses the 2020 return), the option to amend for the impact payments shows up under "Federal Review". But when I try to amend the 2021 return, for the third economic impact payment, something strange happens. When I load the 2021 application, an option shows up to adjust for the economic impact payments, as it did for 2020. But when I load my .tax file, which I understand is necessary to amend the return, this option disappears, and all I get is a list of possible deductions and credits that does not include the economic impact payments. I see no way to amend properly without this. 

How can I fix this? 

Thanks in advance!