Unfortunately, once you have started preparing your returns together with a spouse or partner, there is no way to separate the returns. You would need to create a new return to prepare a separate return.

In TurboTax Online 2017:

To delete a return, select “Return Manger” from the “Tools” menu on the top right. Then click on the trash can icon next to a return to delete it.

If you only have one return, it won’t show the trash can. Click on the “Continue” button after “Start a new 2017 return” to create a blank return. Then select “Return Manger” from the “Tools” menu on the top right. Now you should be able to delete your return, leaving only the empty return in the account.

In TurboTax Online 2018:

Click on “My Account & Returns” at the top of the left side menu, then click the small Trash Can next to the unwanted return to delete it.

If you only have one return, it won’t show the trash can. Click on “My Account & Returns” at the top of the left side menu, then select “Start A New Return” and create a dummy return. Now you should be able to go back to “My Account & Returns” and delete your return, leaving only the dummy return in the account.