You would have to amend the previous years. Didn’t the 1099NEC income show up on Schedule C? Did he have a Net Profit or a loss?
You pay Self Employment tax (Scheduled SE) FICA on a Net Profit of $400 or more on Schedule C in addition to regular income tax on it. You pay 15.3% SE tax on 92.35% of your Net Profit (If it is greater than $400). The 15.3% self employed SE Tax is to pay both the employer part and employee part of Social Security and Medicare.
