What can you use to remove tear stains on dogs?

I rescued my chihuahua close to a year ago and I have been trying to remove the brown tear stains under her eyes. Nothing seems to work. I have taken her to the vet and she has no eye infections of any kind what so ever. He suggested using contact lense solution. That didn’t work either. I have also tried multiple store bought products and no luck there either. Any suggestions? is there something I can make at home that I don’t need to buy?