Salam Alaikom
1- Ask Allah for forgiveness, and pray for that person
2- Estimate the cost of the window and now pay it as Sadaqa (charity) for the poor on behalf of that guy. Say, “O Allah, I give this amount as charity on behalf of that guy.”
3- Let your parents give you the money and you make the intention to pay charity on that guy’s behalf
If you do this then you will have fulfilled your responsibility.