Unfortunately, Form 2678 is not supported by TurboTax software. You would need to print out the form from the IRS website and mail it in.
For the form to print out: https://www.irs.gov/pub/irs-pdf/f2678.pdf
Where to mail form: https://www.irs.gov/uac/where-to-file-your-taxes-for-form-2678
