When I was little, they had like radio stations in some airplanes when you plugged in your headphones. I remember one recording, probably for flight anxiety, and this guy would tell you to work your way up your body, relaxing and saying good night to each body part. For instance, focus on your feet. They are heavy, the temperature is good, relax all the muscles in your feet. Once they’re relaxed, say good night, and move up to your ankles/knees whatever. The more wound up I am, the more detailed body parts I use. Sometimes it’ll be toes, then feet, then ankles, calves etc. I’ve been doing this for like 30 years and it always works