Is it a sin to help a friend study man-made law, and what should be done to atone for helping obtain judicial rulings that are not based on what Allah has revealed?

There is no harm in studying man-made laws if the purpose is sound, such as understanding the superiority of Sharia over them, or benefiting from them in matters that do not contradict Islamic law. However, if the purpose is to implement and promote them while they contradict Sharia, then it is forbidden. And whoever intends to implement them, it is not permissible to assist him; rather, he must be advised. The questioner knows best his friend’s intention; if his intention is sound, then there is no harm in assisting him, otherwise, he must repent and advise him.