What should one who forgot he was not in a state of ablution do, then remembered during the Friday sermon?

If a worshiper forgets that he is not in a state of ritual purity (wudu) and only remembers this during the sermon, then performs the Friday prayer without wudu out of ignorance, he must make up the Friday prayer as a Dhuhr prayer. Every Muslim must learn the individual obligations (fard al-ayn) such as ritual purity (tahara), ablution (wudu), and prayer (salat).