I have already completed my taxes but my son wants me to file his. How do i get an additional copy to file for him

[DoninGA]

Using the TurboTax online editions you can only file one tax return per account and User ID.  To start another tax return using the online editions you would need to create a new account with a new User ID.

Go to this TurboTax website and click on Sign up in the upper right of the screen to start a new account - https://turbotax.intuit.com/personal-taxes/online/file-your-own-taxes/