How do you heat warmer bag without using microwave?

To heat a warmer bag without a microwave, you can submerge it in hot water for several minutes. Ensure the bag is securely sealed to prevent water from entering. Alternatively, you can place it in an oven set to a low temperature (around 200°F or 93°C) for a few minutes, monitoring closely to avoid overheating. Always check the manufacturer's instructions for specific heating guidelines.