If I murder someone and then say michammi dukddam will my sin be forgiven

No.

In Jain Dharma, “micchāmi dukkaḍaṃ” is not a magic sentence that cancels the karmic परिणाम of intentional murder. Himsa done with intention creates very heavy bondage of karma. A true apology must include:

• sincere repentance,
• stopping the violence completely,
• remorse in the heart,
• accepting proper prāyaścitta / atonement,
• and living with restraint and compassion afterward.

If someone commits murder and only says “micchāmi dukkaḍaṃ” without genuine inner repentance and ethical transformation, the sin is not simply forgiven in the Jain sense.

Jainism teaches that karma is removed by true repentance, self-restraint, confession, and penance, not by words alone. Also, the harm to the victim cannot be undone.

If you want, I can explain the Jain meaning of micchāmi dukkaḍaṃ and prāyaścitta more clearly.