What should a person do if they experience frequent wet dreams while performing the Hajj rituals, and they only have their soiled Ihram garments, and is it permissible for them to carry more than one set of Ihram?

Your friend must perform a ghusl (ritual bath) if he has a wet dream. He is not obliged to wash the semen stains from his clothes, because semen is considered pure by Imam Al-Shafi'i, Imam Ahmad, and the majority of scholars. However, if he washes the area affected by the semen, that is better. A person in a state of ihram (ritual consecration for Hajj or Umrah) may change his clothes whenever he needs to.