You can use a shampoo made for dogs, one made for cats, or Dawn dishwashing soap. Make sure whatever you choose is *plain*, not with extra stuff added for scent or softness or stuff like that. And get absolutely all of it out all the way to the skin. The description I've seen for washing a whole rabbit is to use the kitchen sink, fill it with about two inches of lukewarm water, and sit the rabbit in it. Use a cup to pour the sink water over the rabbit as you work the shampoo in, then drain the sink and use fresh water to rinse it out.
Spot washing is just when you wash the areas that need it, rather than washing the whole animal. You would put the rabbit in a dry sink, use something like a wet washcloth with the shampoo on it to work only on the affected areas, and a cup to rinse them.
You may want to try something else first - work some cornstarch into the yellow spots, let it sit for a few minutes, and brush it out. (Use a baby hairbrush if you have short haired rabbits.) Sometimes that works for yellow spots without having to get the rabbit wet. A wet rabbit is NOT a happy rabbit!