Be sure to check for updates so that you have the form as soon as it is available.
If you need to file it before it is available in Turbo Tax, you can print it from IRS.gov and complete it.
I have included a link to the form, instructions, and mailing address information: Form 4868 Extension
Here is a TurboTax Help Topic which will provide additional details: Turbo Tax Help-Extensions, Additional Information