Press Ctrl+Alt+Delete on your keyboard. Select Task Manager. Close the TurboTax program.
@macuser_22 If you are around, are you please able to assist this user? Thanks!
In the meantime, I did find this article on the Apple website, which tells how to force quit on a Mac:
@johannalyman - BTW: what year are you doing? If 2016 than there might be a compatibility issue - post back for a workaround.
If 2018 then I suggest restarting the Mac after force quitting TurboTax.