What is incumbent upon one who broke their fast on several days in past Ramadans due to masturbation, and was intermittent in their prayers during some of those times, and what must they do to repent and rid themselves of this habit?

If you repent with a sincere repentance, it is hoped that Allah will forgive you. If you were ignorant that masturbation breaks the fast, then you do not owe any make-up days. However, if you knew, then you must make up all the days you broke your fast. No expiation (kaffarah) is required of you except for breaking the fast by intercourse. Masturbation is forbidden, and repentance from it is obligatory. Among the things that help with repentance are: marriage, occupying oneself with what benefits them, keeping company with righteous people, reducing free time, remembering Allah, and reflecting on the Last Day.