How do you use hand warmers after you've already used them?

After using hand warmers, you typically cannot reuse them if they are of the disposable type, as they are designed for single use. However, if you have a reusable hand warmer, you can reset it by boiling it in water until the contents return to their original state. Once cooled, you can activate it again by clicking the metal disc inside. Always refer to the manufacturer's instructions for best practices.