there is ..., and thatThis is not a fixed expression: 있는데 means “there is/are” or “have,” often with a contrastive sense, and 그거 refers back to something as “that” or “it.”
KO: 방에 여분의 의자가 있는데 그거 가져다 쓸래?
EN: There’s a spare chair in the room. Would you like to use it?