Click on Federal on the left side of the online program screen
Click on Other Tax Situations at the top of the program screen
Under Other Tax Forms
On File an Extension, click on the start button
Or go to this website - https://turbotax.intuit.com/irs-tax-extensions/
Note - An extension is only for filing the tax return. Any taxes owed have to be paid on or before 05/17/2021 to avoid a failure to pay penalty.