# I will put a spirit in him, and he will hear a certain report and go back to his own land
"I will control the attitude of the king of Assyria, so when he hears a report, he will want to return to his own country" or "I will cause him to think differently." Here "spirit" probably refers to his attitude and thoughts.
# I will cause him to fall by the sword
"I will cause him to die by the sword" or "I will cause some men to kill him with a sword"