As you know, my uncle has some friends in the music world and it was a golden opportunity when he asked me to [help] at the Tina Turner concert!

golden 本义是"金色的"，在这里用作比喻意义，表示"极好的、珍贵的"，强调机会的难得和宝贵。 help 是动词，意思是"帮助、协助"，在这里指在演唱会中提供协助工作。