If the bump on the back of your heel is from a recent injury to the area, the protuberance/swelling typically will resolve on its own. Icing is a great way to try and expedite the process.
On the other hand, if the bump on your heel is from a bone spur, there is unfortunately nothing you can do on your own to make it go away. Once the body has deposited bone in an area, the only way to remove or reduce this bone is with surgery. In instances where this is necessary on the back of the heel, it becomes more complicated than a simple removal of bone, because this bone is covered with fibers from the Achilles tendon. In removing the bone spur, the tendon needs to be carefully removed from the spur and then anchored back to the heel, where it will then need to heal before it is back to its original level of strength. Accommodating this bump and stretching the tendon can alleviate a lot (if not all) of the symptoms associated with the bump, and in these instances (even with the bump still there) surgery can be avoided.