Manufacturer Spiff is not Self-Employment income, but 1099-NEC is.
Either the income is for something else, or the issuer used the incorrect form.
There is no other way to report a 1099-NEC in TurboTax since Form 1099-NEC is for Non-Employee Compensation and to be used strictly for Contractors (Self-Employment).
You might want to contact the manufacturer and ask for a corrected form.