If it's PM, it's easy. If budrot, you're screwed from what I know.
Get a quart of hydrogen peroxide from the drug store. (or a new bottle). Dump that into a gallon container. Top off with pure water. Completely spray the plant down, soaking everything thoroughly. The PM will come back every couple weeks forever, think cancer, herpies or Aids for a plant.
When you harvest, use the same mix. Spray the night before harvest. Cut and trim your buds as always during a harvest. Soak the buds and trim for 15 to 20 minutes in the solution. Set buds on a screen to dry with a light breeze from a fan, and not in the sunlight. Cure as normal.
Bud appearance and quality is indistinguishable from normal.