I'm not sure about any specific supplement to address borderline type 2 diabetes but I started eating healthier after reading Dr. Terry Wahls story and buying her book, The Wahls Protocol - https://terrywahls.com/about/#DrTerryWahls. She now sells vitamins but I haven't purchased any and just not sure I would focus on vitamins unless there was a deficiency and I discussed it with my doctor. Her life story of her symptoms with MS is amazing and I think was mostly done through diet.

Another good one discussing low carb and healthy diet is Dr. Jay Wortman. He has a couple of good videos but I think this one is one of the better ones - Dr Jay Wortman Diabetes Remission is Surprisingly Simple!: https://www.youtube.com/watch?v=Cx6xw3wOAMc