In Jain dharma the main things now are awareness, repentance, and proper resolve for the future.

You can gently suggest your friend to do the following:

1. First see the intention (bhāv):

- If he did not know it had onion–garlic etc. and ate by mistake, the fault (pāpa) is lighter. - If he knew and still ate, then the fault is heavier and repentance should be deeper.

1. Do pratikraman (repentance):

- With a sincere heart, he should mentally say something like: “I have eaten food mixed with ginger–garlic–onion, which is against Jain principles. I repent for this mistake and will try not to repeat it.” - If he knows any formal pratikraman sutras (e.g., Khamāsanā, Micchāmi Dukkaḍaṁ), he can recite them with this bhāv of repentance.

1. Make a clear niyach (vow) for the future:

- Decide: “From now on, I will always check ingredients carefully before eating.” - Avoid packaged items without clear labels. - If outside, ask clearly whether onion–garlic is used.

1. Avoid over‑guilt, focus on reform:

- Jainism teaches us to learn from a mistake, not drown in guilt. - Honest repentance + firm resolve not to repeat is the right Jain way.

1. If he follows a guru / upadhyaya:

- He may also share this openly with his guru and take guidance or a small anuvrat/niyam (like no unknown snacks, always read labels, etc.).

So, in short: Accept the mistake → do pratikraman sincerely → strengthen vows to avoid such food in future. That is the proper Jain response.