You could try doing the 5 Tibetan Rites. They are supposed to restore original hair colour.
Download The Eye of Revelation pdf. or watch YT videos.
But how reliable are they? I’ve been doing the rites for several years and at 68 I still have brown hair and not much grey, but I make no claims. The rites should take 6-10 minutes to perform and may be equivalent to doing over an hour of yoga.
You have to overcome the first rite which is a spinning exercise not suitable for everybody, so be careful.
Many claims have been made for the health benefits of these, and the person who discovered them, assumed to be Wilfred Malleson, lived to 80.