It might be possible to shrink blue jeans using boiling water and heat, but some blue jeans are made using materials that are sanforized that won't shrink more than 1 percent. Blue jeans made with raw materials that haven't been sanforized are the blue jeans that usually respond well to efforts to shrink them.
Placing the blue jeans in boiling water or in the hottest water possible in a washing machine might help them to shrink. It is essential to keep the water hot, so it must be changed every 10 minutes for an hour.
Drying blue jeans in a hot dryer might also cause them to shrink. If the jeans need to fit a person's curves, taking them out while they are damp, yet almost dry and putting them on might help this to occur, as long as the wearer doesn't sit down until they are dry.