Please read this TurboTax FAQ for information on "How do I file an IRS extension (Form 4868) in TurboTax Online?": How do I file an IRS extension (Form 4868) in TurboTax Online?
The above answer is correct and you should file an extension of time to file (not pay), but you may still file late if you do not file on time.
https://turbotax.intuit.com/tax-tips/irs-tax-return/video-filing-taxes-after-the-april-deadline/L0Jl6YQ2B