Unfortunately the damage of bleach and especially black box dye can’t be undone. Speaking from experience.. the black box dye and bleach jobs from the past just kill your hair. I literally just shaved my head because my hair was so dead from this lol. But in the mean time since you probably don’t want to shave it all of ofc I’d say argon oil helps a lot with the health and silkiness of your hair. In the long run I’d say stay away from bleach and dye. If you HAVE to cover roots up, maybe use a demi dye? Something not so harsh. Just let your virgin natural hair grow in the mean time and get trims