What can I do to make the swelling go down from my dog's lip/ soft tissues to the side of mouth)?

My dog had ingested some chocolate brownies today & the vet told me to give her hydrogen peroxide to induce vomiting before the toxins enter her system. I repeated the procedure the vet suggested 3 times. & now in the evening I find that corner fleshy part of my dogs mouth is swelling up & the vet is closed & so is the animal hospital.