What can i use to kill yeast on my bottom lip and corners of mouth?

A few things: Are you sure it's yeast? Not all white residue is yeast . Yeast would likely burn, and not be confined to the corners of your mouth. If it is, a very mild vinegar would likely be the simplest thing. Yogurt would be another home remedy that might work. Otherwise a prescription for Nystatin mouth rinse or Clotrimazole troches would be used.