My usual answer to this question is to go back and prevent my parents from meeting, even if it means killing one or both of them. Yeah, I’m not a happy camper, and rarely have been so in my nearly 50 years.
Right now I’m not feeling all that well and I’m pissed about some other things, so I might go all the way back to The Toba supereruption.
I would see to it that those survivors didn’t. More and more I come to the belief that the world would be better off without humans.