If a plant is in soil that is water-logged, it is best to determine why. Was there no drain hole? Is someone else watering your plant? Is the plant in a pot that is too big or in light that is inadequate? Simply replacing the soil with dry soil is not a very good solution and may cause a lot of other problems.
Bagged potting mixes often contain non-sterile ingredients such as bark chips, soil, and compost all of which may contain fungus spores and fungus gnat larvae. This is a potential problem even if the bag is fresh off the retailer's shelf. Look for a potting mix that contains only peat moss, coir, perlite, lime and some fertilizer. Unfortunately, you have to find the ingredients and they are in fine print on the bag. As an alternative, you can mix your own by using 4 part of peat moss and 1 part perlite.
