The TurboTax software for tax year 2017 only supports Mac OS X v10.11 or later (64-bit required)
See this TurboTax support FAQ for the Mac minimum system requirements - https://ttlc.intuit.com/questions/1899173-minimum-system-requirements-for-turbotax-mac-software
Go to this website to request a refund of the software purchase - https://support.turbotax.intuit.com/forms/refund-request.jsp
If you do not want to or can update your OS then you can use the TurboTax online editions - https://turbotax.intuit.com/personal-taxes/online/
