Just a little drying out will take care of that.
Although that is true, I know it doesn't mean much to a newer gardener.
--- What the heck does "a little drying out" mean?
When your potting soil is dry enough so that it doesn't stick to your hands, and doesn't stick together because of wetness... that is dry enough. Sunshine is not needed. Sun rays will hasten the death of the mold, but will also hasten the death of good soil organisms in the soil, too.
Cinnamon is sometimes tried as a surface application for certain unwanted fungi that grow at the soil surface. One could only assume that a "sprinkle" would be like a sprinkle of pepper on your food?
But that would do nothing mixed into the soil. If you were going to mix it into the soil, say, a gallon by volume, you would need a quarter teaspoon or more.