There may be a very simple solution to your issue. If your foreign financial account(s) has a negative balance, and did not at any day during the year exceed the filing threshold dollar amount necessary to mandate disclosure reporting . . . then you can simply indicate to the TurboTax software that you had no such foreign account at all. This would be consistent with the underlying tax laws, which only requires disclosure and reporting of accounts that are more valuable than certain dollar levels; and it would not require you then to upgrade to the TurboTax Deluxe (or higher) software version.
In the absence of that, you may indeed be required to upgrade TurboTax versions from the Free File edition, or to find an alternative method to file your income taxes.
In fact, there are two separate disclosure forms that may be required of US taxpayers who hold foreign financial accounts; each also has different reporting rules. One is known as IRS Form 8938, and can be attached to the relevant yearly Form 1040 tax return. The other is FinCen Form 114, which can only be filed via the internet. The following Internal Revenue Service webpage describes them in some detail, and provides their dollar value reporting levels:
Form 8938 is included in TurboTax. FinCen Form 114 is not included in TurboTax, and you would need to access that reporting webpage separately, if your foreign financial assets total over the limit(s). Note that you can get to the FinCen reporting internet site directly through the above IRS link.Thank you for asking this important question.