It is my understanding that yorkies have human-like hair, that being said, I know nothing can repair breakage or split ends on our hair, the only solution is to cut all the damage off, or cut up to the shortest break as mentioned previously. Start fresh, applying topical products doesn't help hair to grow faster*, good, healthy diets, rich in omega-3's does, but results may take up to 3-6 months.
I have a friend that attempted to save money by coloring and highlighting her own hair, not only did she damage it, she told me the professional corrective coloring ended up costing her double what she would have paid to begin with.
You mentioned, you now know what you have done wrong, maybe you should do more research
before embarking on uncharted territory or seek professional help, especially on something that seems to be very important to you. Good luck and remember, its just hair...it will grow back
*With the exception of minoxidil and copper peptides which are applied directly to the scalp, not hair. Neither of which are safe to use on dogs.