When you're ready to file, simply open your return in TurboTax, finish your return, and file it as you would normally do.
You don't need to do anything special unless you made payments with your extension. In that case, follow these instructions to get credit for the payment:
1. In TurboTax, search for the exact phrase estimated tax payments (if necessary, copy/paste from here).
2. In the search results, click Jump to estimated tax payments.
3. On the next screen, Estimates and Other Income Taxes Paid, click Start next to the Payment with 2015 federal extension topic.
4. Follow the simple on-screen instructions to enter your federal tax payment.
5. (Optional) When you get back to the Estimates and Other Income Taxes Paid screen, you can also enter any state or local payments you made with your extension.
6. When done, click Done with Tax Payments.
Once you've done that, finish your return and file it before the October 17 extension deadline.