@cohjahk,

There is no way who has already moderated. But you have a way to let certain moderators moderate certain forums. You should use Forum Accesses, Usergroups and Secondary Usergroups. Read this topic to understand how all those work then you can create new Moderator usergroups and let them to moderate in certain forums: https://wpforo.com/community/faq/wordpress-user-roles-wpforo-usergroups-and-forum-accesses/