Please follow below mentioned clean-up steps & try application update again.
1. Close TurboTax Premier 2017 application by pressing Command + Q keys.
2. Single click on empty area on Desktop and press Command + Shift + G keys. Type ~/Library in text field and click "Go".
3. Now, navigate to "Caches" directory and remove "com.intuit.turbotax.2017" directory under it by by dragging it to Trash.
5. Empty Mac OS Trash directory by right click on Trash Icon and select "Empty Trash" option.
6. Restart your mac machine. Check internet connectivity on you machine.
8. Launch TurboTax Premier 2017 application by navigating to /Applications directory.
9. Let Product & Formset update to download & install, if available any.
10. It should address your problem.
