On Monday, the Iranian team beat the Koreans 3-0 (25-22, 25-21, 25-19) in Riffa, Bahrain.
Iran had defeated China 3-0 in its first match on Saturday.
Iran will play winner of India and Hong Kong on Wednesday.
The 2018 Asian Men's U-20 Volleyball Championship kicked off on July 21, and will run through July 28.
The top two teams of the tournament will qualify for the 2019 FIVB Volleyball Men's U-21 World Championship as Asian representatives.