I had this same problem and emailed the company for suggestions. They said to use 5 tsp of water mixed with 1 tsp of white vinegar and apply with a soft cloth. This worked on some areas of my quilt but not on others. Please try it first on a hidden area of your quilt to make sure it doesn't change the fabric color (it didn't when I used it). I also used a soft tooth brush on stubborn areas and this seemed to work better than the soft cloth.
Good luck--this is so frustrating!!