How can one atone for masturbating while fasting, for someone who did not know that this act is masturbation, and how can one be cured of this practice?

What that traitor did is among the grave sins, and it is a result of families' laxity in observing religious matters, such as allowing a non-mahram man to enter the home in the absence of the master of the house, being lenient with unlawful seclusion (khalwa), and women displaying their adornments before non-mahram men.

Masturbation is forbidden, and whoever commits it must offer sincere repentance from it. Its remedies include lowering the gaze, avoiding living alone, increasing fasting, remembrance (dhikr), and supplication (du'a), associating with righteous people, and striving for marriage.

To learn about the rulings concerning masturbation during the daytime in Ramadan for someone who knew of its prohibition, or for someone who did it out of ignorance of its ruling, previous fatwas can be consulted.