Solved
For tax year 2015, I filed an extension in April 2016 but haven't yet finished the return nor submitted. I suspect that I need to complete this by downloading the 2015 software, but I'm on a Mac. Is this available? Thanks for any suggestions.
Yes, you can download the TurboTax 2015 for a mac computer.
Go here and click on "Buy Now" under 2015, you will then be able to select Macintosh.
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