How do I mark my taxes as finished because they have been done somewhere else

It cannot be done and it is not required. 

Well certainly do not file them from Turbo Tax.  You can just abandon this return or try to clear it out.  If you haven't filed, registered or paid you can try to clear
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-online/00/26444

In order to get your return to the finished state, use the FILE step.

You have to pay the TurboTax fee.