The option to pay your TurboTax fees from your federal refund is given in the first step when filing. It will ask "How would you like to pay for your TurboTax?"
This link would be able to assist you with how and where to select that option:
Pay With My Refund
This link will help with the situations where you would not be able to use Pay With My Refund:
Can't Pay With My Refund