How do i reform to be able to hextech craft?

You reform by playing games without being meaningfully reported.

I know that's kinda vague, but that's really all there is to it.

You basically have to own the champion who you are trying to get a chest with, and you must get a grading of S, -S or +S

I hate to be the one who says this, but it will be approx three months of good behavior before you can. That's not a guarantee either, it could be a bit less or a bit more. They randomize it around that point, so people can't just be good to a set date/then fall back to there old ways.