It sounds like you are attempting to upload your 2020 tax file into the "Online" software to amend your 2020 tax return.
You Can't do that ! Online is only for 2021 taxes, not 2020.
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To amend your 2020 tax return, you restart your already installed Desktop 2020 program, and amend from there. Yes, the .tax2020 file has to be in there already, but perhaps the desktop program has the proper path to it and it will show as soon as you start up the 2020 Desktop program. IF not, then yes, you'll have to recreate the original...Save it, then amend it.
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IF the original file doesn;t show when you start yoru desktop program, Search for that .tax2020 file !
Look in the trash folder. And if you have a cloud service for backup files, check that too. Tose tax files simply do not disappear unless you purposely/accidentally erased them.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
