It means that he or she will do the work.

I means "don't give him the answer" or "let him figure it out him self"

一个人担心或紧张时就会流汗。所以 "Let him sweat" (让他流汗) 的意思是让他继续担心。 比方说你恐吓你的朋友说你会偷他的车子。其实你不会的，但你不告诉你的朋友，反而你故意让他担心。你跟你的弟弟说："I'm going to continue letting him think I will steal his car. I'm going to let him sweat!"

заставить его вспотеть...))

这要看语境