DIAGNOSIS The water isn't getting cold enough before the freeze cycle triggers, so you get a thin sheet of ice instead of a cube. The most common cause is the ambient room temperature being too warm.
FIX Move the ice maker. It needs to be in a room under 77°F (25°C) and away from direct sunlight, ovens, or other heat sources. Also, make sure the rear ventilation grill has at least 6 inches of clear space. Let it run for a full 24-hour cycle in a cooler spot to see if cube size improves.
IF THAT DIDN'T WORK The internal thermostat might be faulty. Unplug the unit, empty the water, and let it sit for an hour to reset. Plug it back in with fresh, cold water and try again.
HEADS UP These are thermoelectric coolers, not compressor-based. Their cooling power plummets in a hot kitchen. They work best in an air-conditioned space or a cool basement.