Contributions may be limited if total income (from all sources) is too high, but the contributions can only be made from compensation (income earned from working), either W-2 wages or self-employment.
To avoid a penalty, you would have to remove the excess by the filing deadline with extensions. Since the plan probably can't process a withdrawal in a couple of hours, I suggest you get the automatic extension online today. Then, contact the broker to remove the excess. You must also remove the earnings that can be allocated to the excess contribution (the broker knows to do this). Those earning are taxable on this year's (2023) return even though you will get a 1099-R next year. Report the withdrawal of excess by entering a "fake" 1099-R with the total withdrawal in box 1, the taxable earnings in box 2a, and use codes P and J in box 7. The excess earnings are subject to income tax but not a penalty.
Or,
Leave the excess in the account and pay a 6% penalty. Then in 2024, make sure his Roth contribution are at least $148 less than his maximum would otherwise be. That will cause the 2023 excess to be applied to the 2024 limit. By "using up" the excess in 2024, there will be no further penalty.
