If you are using the CD version of TurboTax Premier, a return is all prepared offline in the installed software.
So hopefully you are not using an Online TurboTax account to prepare your return and the friend's return by mistake. With the CD version, you do not need a browser and do not need to sign into any online account.
ADDENDUM: The instructions I provided below are for the Windows version. If you are using the Mac version, then see VolvoGirl's comment below on how to start a new tax return in the Mac version.
In the Windows desktop software to start a new tax return for another person, launch the TurboTax software. At the main screen, go to the top left corner of the TurboTax user interface and click on FILE, then in the dropdown menu choose New Tax Return.
The program will churn a bit as it searches your computer for any *.tax2017 data file from last year. If it finds one, it will ask you if you want to transfer it in. If it's YOUR 2017 data file, then decline to transfer it, or your info will transfer into your friend's return. However, if you happen to have your friend's *.tax2017 data file from last year, then you can transfer it into the friend's new return. Otherwise, click to continue without transferring.
