You would report this interest income exactly as if it was reported to you on a Form 1099-INT, in the Interest on 1099-INT interview of Personal > Personal Income > Interest and Dividends.
I believe in the case of a 1099-INT from a PRIVATE PARTY or if the 1099-INT DOES NOT EXIST then you may have to IGNORE the TurboTax Mis-guidance in the question "Do you have any interest from ANOTHER BANK OR BROKERAGE?" (if/when that question comes up. YMMV. )
I think you say YES here even though it is NOT from a "bank or brokerage".
Plenty of other places interest might come from, TT!!