Missing Jumua Salaah

Recently my small brother left juma prayers (as he was sleeping and when he got up he realized that he missed the juma prayers). There was nobody in the house at that time to wake him up. Our parents do not live with us, we live alone. So there is no one in the home accept my brother. He told me yesterday that this was the third time he missed juma prayer. I read a hadith stating that if you leave juma for three consecutive weeks you will become a kafir. I told my brother this Hadith, he is very worried, because he thinks he is not a Muslim any more. He promised me that he will not repeat this. He wants to atone for his mistake and remain a Muslim till his death. What should he do at this point?