You cannot e-file a Form 4868 extension request using TurboTax until later in March.
Go to this Easy Extension website - https://turbotax.intuit.com/irs-tax-extensions/
If you would prefer to file an extension now you will need to print and mail the Form 4868 to the IRS.
Go to this IRS website for the Form 4868 - https://www.irs.gov/pub/irs-pdf/f4868.pdf
