How can one repent and atone for the rights of the imaginary girls during masturbation?

Masturbation is forbidden and repentance from it is obligatory. Scholars have differed regarding the ruling on a husband imagining a specific foreign woman during intercourse with his wife; some have said it is forbidden, while others have permitted it. According to the view that it is forbidden, it becomes more severe if accompanied by masturbation. The questioner is not obligated to do anything regarding the imagined girls. The prohibition here is to block the means (sadd al-dhari'ah), as Sheikh Ibn Uthaymeen explained, because thinking about a specific woman can lead to temptation. One must repent, seek forgiveness, and abandon this blameworthy act.