Two main reasons that can cause mold are overwatering and too much warmth. So it's very important that when you add water, the float shouldn't rise above the surface of the lid. We would recommend that the float should stay in the middle of the tank. If your plant pods still seem too wet (which cause moss and mold), just click the pods out of the garden for 1-2 days to let them dry. Also, make sure that the temperature inside your home is okay for the plants. The best average temperature to grow your plants is 18 to 24C (64 to 75F).
You can also try to scrape off the mold but gently as to not damage the plants or seeds. The plants (seeds) will still be okay to grow and use after the mold has been removed.