How is an infidel who embraced Islam then committed an act that nullifies Islam out of ignorance to be treated, and is he required to renew his Islam?

He should be treated with the best conduct, and it should be explained to him that his action is one of the nullifiers of Islam. He does not need to renew his Islam due to his ignorance of what nullifies it, as Allah Almighty says: (And never would We punish until We have sent a messenger) Al-Isra/15, and His saying: (And never did We destroy the cities until their people were wrongdoers) Al-Qasas/59. The ignorant person is not a wrongdoer, especially if he is new to Islam.