Talk to Psychiatry on >Going Over And Over Something That Happened 50+ Years Ago

He's stuck with a trauma happened 50+ years ago. He made choices then, I dont know unknowingly and without sane thinking, that he how repents and wants clarity. I've told him that it's not achievable as every one around that trauma incident has either passed away, isn't around or (considering age factor) may not be able to give accurate details. How do I convince him to get help? and if he doesnt agree for medical (Psychiatric) help, what are my options?