Arm bend on a clean is, IMO, the single hardest thing to fix with a lifter, because the lifter has to fix it themselves. Some things we try: HARD internal rotation of the elbows (Look up internal rotation / external rotation before you to this - 50% of people get it 100% wrong); Think about pushing the bar down when you jump; lock your triceps down HARD, etc.
Unfortunately we're not there to yell at you. You know you're doing it. Make yourself stop!