He hasn't done anything. It's the new South Korean president that's enabled progress there. At best I guess you could say Trumps eagerness to be a difference maker maybe means he's much more willing to meet with Kim and 'get on with it', but prior to that his North Korea 'policy' was being a twitter troll.
He's attempting to take Iran out of the fold again and fucking up progress made on that front, he's starting trade wars, relations with Russia are at a low. The less said about Jared's progress on the Israel/Palestine front the better.
The best thing you could probably say about it is that his impact has been pretty limited despite his best efforts.