Leftover fondue can be stored in an airtight container in the refrigerator for up 4 days. To reheat, transfer the fondue to a microwave-safe bowl and heat it in short, 15-second intervals, stirring between each interval to ensure even heating. Alternatively, you can reheat the fondue on the stovetop using a double boiler or a similar setup to gently melt the chocolate. Reheat only the amount you plan to use, as repeated reheating may affect the fondue's texture.