I painted latex in a bathroom that I didn’t know had oil based paint on it. Now it is bubbling and I want to fix it. How do I fix the bubbling paint?
Scrape off the bubbles and any loose paint. This won't be easy as the paint is soft and rubbery. Prime the damaged areas with a quick drying oil based primer, Kilz or Zinsser Cover Stain, then skim over these areas with a little drywall mud (after the primer has dried). Sand the patches, prime again (spot priming) then touch up with your paint.
The is a good changes that this could happen again on the areas not removed, not bubbling right now. You will have to fix bad areas as they occur.