You can fix it with a texturing technique that drywall installers call skim coating, which is a method they use to create perfectly smooth walls. While it doesn't involve complicated tools and supplies, it takes a certain amount of skill to do it right.
How do you fix a drywall bulge?
Use your drywall tape to cover any cracks in the bulge, and spread a thin coat of drywall compound over the tape; allow it to dry, and apply another coat. Use your sandpaper to sand the repairs smooth.