The first thing that occurred to me of course was to put an end to all suffering. But you can't really get too far with a plan like that without turning the entire world into a nanny state, and even then you can't control what's going on in people's heads without, well, controlling what is going on in people's heads. So what I'd do, then, is to simply close out the chapter. I'd basically just elevate everyone to a new unphysical plane of existence where they couldn't harm themselves or each other. If there happened to be anyone who was so fucked in the head that they couldn't bring themselves to embrace this new and better existence, I'd just segregate them for a while until they came to their senses. Being God I'm pretty sure that I could get them to come to their senses eventually without completely remodeling them from scratch. I'm the ultimate psychological therapist you see, and I can sell ice to Eskimos.