Mix baking powder and water together and spread over the area of mold. To prevent further mold from growing keep your yard dry and test the balance of your soil.
You will need to create a bleach and water solution. The mixture should consist of twenty percent bleach and eighty percent water. You will need a spray bottle or sprayer to spray on top of the grass. You should spray the grass and monitor to see if another treatment is needed in the future.
Somebody once told me that if you hook a hose up to a sprayer and mand a solution with like 6oz of beer and 1 tsp. dishsoap it works really well on mold growing in your lawn.
You can find various products at your local home depot or lowes. Make sure to choose the right product pertaining to which ever kind of fungus you have and the severity of it.
Lime will usually do the trick and along with getting rid of the mold it will fertalize your yard I have also known of people using boiling water or apple cider vinegar pouring it straight on it and they say that will kill it also I hope this really helps.
too much water, or soil is too heavy. add sand if soil needs it, dig a trench to drain, or sow grass and plants adapted to dampness, depending your climate.