Sprinkle baking soda in the smelly bedroom slippers. There should be a thick layer of baking soda on the inside of the slippers.
Let the baking soda sit for several hours. The baking soda will absorb the odors. Shake the slipper over the trashcan to discard the baking soda.
Repeat the process if the odor is still very strong.
Stuff the shoes with dryer sheets. These will help bring a pleasant odor to the shoes.