TurboTax does not support IRS Form 3520. You file the form 3520 separate from your federal tax return.
Go to this IRS website for form 3520, Annual Return To Report Transactions With Foreign Trusts and Receipt of Certain Foreign Gifts -https://www.irs.gov/forms-pubs/about-form-3520 - https://www.irs.gov/forms-pubs/about-form-3520
Mailing address -
Internal Revenue Service Center
P.O. Box 409101
Ogden, UT 84409
