i do this whenever i have relatively new tires and a wrecked rim. i have an inexpensive water heater that you plug in ac power then dip it in a bucket of water. when the water starts boiling (after about 5 to 10 minutes), i put the tires & rims in for about half an hour. then i dip it in tap water until theyre cool to hold. the tires are easily removed but it helps to have a blade cutter to clean up the rim and tire. then i reuse the tire on a new rim
i think "simmer" means to set the stove to low heat after the water boils. the water will still be hot but not boiling anymore.