Is reciting istighfar obligatory if one makes a mistake in reading the qur'an?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If a person makes a mistake while reciting the Quran and changes a verse of mercy to a verse of torment, or the like, then he is not obliged to seek forgiveness. Asking forgiveness is obligatory only when one commits a sin, as for an intentional mistake, then the person is not held accountable for it. The Messenger of Allah said: "Allah will forgive my Ummah for mistakes, forgetfulness and what they are forced to do."

Although seeking forgiveness is not obligatory if the reciter did not deliberately do the mistake, but this does not mean that it is not permissible to seek forgiveness for this. Rather, it is permissible and the Prophet used to seek forgiveness much, despite the fact that Allah has forgiven what preceded of his sins and what will follow.

Allah knows best.