1. Crack. If it runs vertically down the back, its not too important. Leveling off this stave for bamboo backing would probably be more than you'd want to get into. You can work in some carpenters glue and clamp. It that area needs to be heat treated for twist, wait till after. If its a horizontal crack, report back for another strategy.
2. Twist. BL responds well to dry heat. If you don't have a heat gun, you can use a range top burner or a grill burner. Heat the belly side a few inches away (you can get closer when you know what you are doing) get it uncomfortabley hot to touch and then a little more - a touch of scorch. Secure in vise. Clamp two wood slats, 1/2" x 2" x 20" long of so out past twist and use to gingerly lever in place. Thats one strategy.
Dave