All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
All you have to do is to continue reciting the Quran on this person who is possessed by Jinn, and he will be cured, Allaah willing. Allaah says (what means): {And We send down from the Quran that which is a healing and a mercy to those who believe (in Islamic Monotheism and act on it.} [Quran 17:82]
For more benefit about the legislated Ruqyah and how it is performed, please refer to Fataawa 82917 and 88660.
Allaah Knows best.