Follow these steps:
your return in TurboTax Online.
(To do this, sign in to TurboTax and select the Take me to my return button.)
2. Select File an extension at the bottom of the column on the left side of the screen.
3. If you don't see the File an extension button in Step 2 above, search for extend in the upper right and select the Jump to link at the top of your search results.
4. Follow the onscreen instructions to e-file your extension.
For more information and the source, follow this link: How to File an Individual Extension