What is the correct course of action for a 21-year-old young man who practices masturbation when looking at girls, despite his diligence in reciting the Quran and praying, and these thoughts persisting in his mind?

Looking at girls with the intention of deriving pleasure is forbidden, based on the Prophet's (peace be upon him) saying: "Do not follow a glance with another, for the first is permissible for you, but the second is not." And based on Allah's (the Most High) saying: "Tell the believing men to reduce [some] of their vision and guard their private parts. That is purer for them. Indeed, Allah is Acquainted with what they do." (An-Nur 24:30). Forbidden glances lead to other forbidden acts, such as masturbation.