Originally Posted by airsteve172

The fix for this is actually quite simple!
Make up a sanding block that's about 1"x 2", tightly wrap some #600 wet sandpaper around it, wet the sandpaper by dipping it in some water and gently sand the run until smooth while keeping the sandpaper wet. A drop or two of soap or dishwashing liquid can be added to the water for better lubrication.
After the surface is sufficiently level and smooth, repaint the part, being careful not to cause a run this time!