The basic thrust of Plantinga's argument is that God is not all-powerful (omnipotent); He cannot create a world where free will exists and not allow them to choose between evil or good. He doesn't specifically address the conflict between foreknowledge and free will, but it is implied that God lacks such foreknowledge (he is not omnipotent) because otherwise it could be argued that free will couldn't exist (in a universe in which there is only one possible future).
A world containing creatures who are significantly free (and freely
perform more good than evil actions) is more valuable, all else being
equal, than a world containing no free creatures at all. Now God can
create free creatures, but He can't cause or determine them to do only
what is right. For if He does so, then they aren't significantly free
after all; they do not do what is right freely. To create creatures
capable of moral good, therefore, He must create creatures capable of
moral evil; and He can't give these creatures the freedom to perform
evil and at the same time prevent them from doing so. As it turned
out, sadly enough, some of the free creatures God created went wrong
in the exercise of their freedom; this is the source of moral evil.
He concludes with:
The fact that free creatures sometimes go wrong, however, counts
neither against God's omnipotence nor against His goodness; for He
could have forestalled the occurrence of moral evil only by removing
the possibility of moral good.
This is patently wrong, however. Of course it counts against his omnipotence. Either God can do anything, or he can't. Omnipotence is not up for debate.
So he doesn't actually resolve the conflict. The Problem of Evil, I'm afraid, is still a problem.