I think some things you can't fix, no? How about the fact that we're all going to die one day and there's nothing we can do about it and there's probably no afterlife? That kinda bums me out and makes me sad. Would be nice to not have random negative intrusive thoughts, but I'm not sure if that is something that can even be fixed.
It can, you just have to accept that we all only have 1 life to live and we gotta live it as best as we could.
How you get to accept that? I personally cant help you with it, cause it's never been an issue for me.