Within the TurboTax program, you will only be able to pay by mailing a check because the 1040X form does not provide ability to direct debit. However, you can easily pay online through the IRS Direct Pay site below - its free and when you make a payment it will ask what the payment is for and you can indicate Amended Return and 1040X.
https://www.irs.gov/payments/direct-pay
If you would rather use a credit/debit card, you can find that option below -