Is it a condition for repentance to inform the young man who was bewitched of what was done to him?

If the rights are material, they must be returned. As for immaterial rights, such as backbiting, there is no need to inform the person concerned; rather, seeking forgiveness for them is sufficient. This applies to harming the young man through trickery and magic, where you are not required to inform him of what you did to him. Fulfilling the conditions of repentance is sufficient. However, if the young man or others become aware of what you did, then you must apologize to him and ask for his forgiveness.