Iran had previously defeated Tunisia 3-0 and the Czech Republic 3-0 and lost to Russia 3-2 in the pool.
Iran will play Italy on Tuesday.
The 2019 FIVB Volleyball Men's U-21 World Championship is being held in Riffa, Bahrain from July 18 to 27.
A total of 16 teams from the 5 confederations compete in the tournament.