Fondant can be heated directly in a saucepan but to help avoid over heating, warm it over a bain-marie (water bath) to slowly heat it. It should be heated to a little below blood temperature, 32-35°C (90-95°F).
You may also need to adjust the consistency a little by adding syrup to soften and make it a good workable consistency. The consistency should be fluid but thick enough to hold its shape for a moment when the mixture is poured into the rest of the fondant. To maintain a soft smooth consistency and attractive sheen, do not overheat the fondant - otherwise the fondant has a tendency to crystallize.