the word saw is the suitable word it should be using here, cause the word yesterday had clarified the time which is past simple, cause if we choose have seen that means we will not need to the word yesterday which located in the end of the sentence as the rule says.
but with yesterday we use the simple past tense.
for example we can say I saw King of Darkness yesterday.
I have seen King of Drakness.
I think you're right...... now a see, so the correct answer would be
I saw him yesterday.:up:
because of the specific time