How do you warm up someone with hypothermia?

How do you warm up someone with hypothermia?

Treatment

Seek immediate medical attention for anyone who appears to have hypothermia. Until medical help is available, follow these first-aid guidelines for hypothermia.

First-aid

Be gentle. When you're helping a person with hypothermia, handle him or her gently. Limit movements to only those that are necessary. Don't massage or rub the person. Excessive, vigorous or jarring movements may trigger cardiac arrest.

Move the person out of the cold. Move the person to a warm, dry location if possible. If you're unable to move the person out of the cold, shield him or her from the cold and wind as much as possible. Keep him or her in a horizontal position if possible.

Remove wet clothing. If the person is wearing wet clothing, remove it. Cut away clothing if necessary to avoid excessive movement.

Cover the person with blankets. Use layers of dry blankets or coats to warm the person. Cover the person's head, leaving only the face exposed.

Insulate the person's body from the cold ground. If you're outside, lay the person on his or her back on a blanket or other warm surface.

Monitor breathing. A person with severe hypothermia may appear unconscious, with no apparent signs of a pulse or breathing. If the person's breathing has stopped or appears dangerously low or shallow, begin CPR immediately if you're trained.

Provide warm beverages. If the affected person is alert and able to swallow, provide a warm, sweet, nonalcoholic, noncaffeinated beverage to help warm the body.

Use warm, dry compresses. Use a first-aid warm compress (a plastic fluid-filled bag that warms up when squeezed) or a makeshift compress of warm water in a plastic bottle or a dryer-warmed towel. Apply a compress only to the neck, chest wall or groin.

Don't apply a warm compress to the arms or legs. Heat applied to the arms and legs forces cold blood back toward the heart, lungs and brain, causing the core body temperature to drop. This can be fatal.

Don't apply direct heat. Don't use hot water, a heating pad or a heating lamp to warm the person. The extreme heat can damage the skin or, even worse, cause irregular heartbeats so severe that they can cause the heart to stop.
https://www.mayoclinic.org/first-aid/first-aid-hypothermia/basics/art-20056624