2016 .tax file

I need to access my 2016 .tax file in order to amend the return. I prepared the 2016 and 2017 tax returns using one username/login; however I changed accounts for 2018 and 2019. The site is telling me that I can't download the 2016 .tax file because I didn't use TurboTax for 2018, only I did, just under a different username. Help?