How can I repent for disobedience to parents according to Islam?

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.

Being undutiful to one’s parents is one of the greatest sins.  Abu Bakrah narrated by from his father that the Prophet said: “Shall I not inform you about the greatest of the major sins?” They said, “Indeed do so, O Prophet of Allah!” He said, “To associate partners with Allah, and to be undutiful to one’s parents.” He was leaning, so he sat up straight [to show the importance of what he was going to say next] and said, “And beware of false speech and false testimony, beware of false speech and false testimony.” He kept repeating it until we wished that he would stop.” [Al-Bukhari and Muslim]

However, if a person repents sincerely to Allah, by giving up the sin, regretting what had happened, and being determined not to commit the same sin again, then Allah will accept his repentance (forgive him).

Allah Says (what means): {Say, “O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.”} [Quran 39:53]

Besides, Ibn Mas’ood narrated that the Prophet said: “A person who repents from the sins that he has committed is like a person who has committed no sin.” [Ibn Maajah]

The method of repenting from this is to be close to your parents, obey them in whatever good they order you to do, seek their pleasure, and do other things by which you gain their kindness and forgiveness.

In case your parents passed away, then repenting from being undutiful to them will be by supplicating Allah to forgive them and have mercy on them, giving charity on their behalf, and keeping good relationship with their relatives, and so forth.

Allah knows best.