بسم الله الرحمن الرحيم
If there is no obstacle, the parents should marry their children finding out any suitable proposal when they are grown up and reach to the age of marriage. In-shaAllah, it shall change his mode. Also recite the following dua in the evening and morning 41 times and blow it on water and give him to drink:
وَالْكَاظِمِينَ الْغَيْظَ وَالْعَافِينَ عَنِ النَّاسِ .
Allah knows Best!
Darul Uloom Deoband