The instructions for Form 1099-R explicitly say that an HFD is to be reported as a regular IRA distribution. A regular distribution from a traditional IRA must be reported with either code 1 or code 7, depending on the IRA owner's age, and with the IRA/SEP/SIMPLE box marked.
Code G with the IRA/SEP/SIMPLE box marked is only to be used for a direct rollover from a traditional IRA to a qualified retirement plan (401(k), 403(b), 457(b) or the federal TSP). TurboTax knows this and will properly not provide any way to indicate that a distribution reported with code G is an HFD.
Contact the IRA custodian to obtain a correction. They need to issue a corrected code G Form 1099-R showing $0 distributed and issue a proper original Form 1099-R with code 1 or code 7 showing this distribution. You'll then ignore the code-G Form 1099-R and enter only the proper code-1 or code-7 Form 1099-R.
