I prayed with a friend dhuhr and I was imam then I realized that I had intention of asr not dhuhr. Then I switched my intention to ratiba of dhuhr because of that. Is my friends dhuhr prayer valid?

The prayer of the one behind him is valid. The invalidity of the imam's prayer does not invalidate the prayer of the ma'mum who is excused. However, I believe that you suffer from waswas so never ever do this again, just continue your salah.