Sanders can do an executive order, but before he does he can do that he knows he's gonna have to at least try and work with congress first. Otherwise it's a pretty quick way to wind up as a single-term PotUS, And he will definitely want to do two terms in order to effect the kind of change he wants.
So, I'd imagine that he'd work at tweaking the free trade agreements - maybe try something that makes it a little harder to export American jobs. He's got his work cut out for him, though - as I've said before, you can't reverse job migration while maintaining your standard of living. He'll have much better luck reforming corporate taxes, healthcare, immigration, and making college free for Americans.
So, I'd imagine that he'd work at tweaking the free trade agreements - maybe try something that makes it a little harder to export American jobs. He's got his work cut out for him, though - as I've said before, you can't reverse job migration while maintaining your standard of living. He'll have much better luck reforming corporate taxes, healthcare, immigration, and making college free for Americans.