With great skill!
A corn is due to there being too much pressure (and maybe a bit of friction) over a small area. In response to that pressure, the skin becomes thicker to protect itself. This is a normal process. However, if the excessive pressure continues the skin will eventually become so thick that it becomes painful.
A podiatrist can use their skills to accurately debride the corn and remove it. It is not actually that difficult. HOWEVER, it is one thing to remove a corn (by whatever method), it is another thing to stop it coming back. The corn will come back unless the cause of the corn is dealt with. They do not come back becasue the Podiatrist did not do a very good job or because the corn has roots (they don’t).
Here is a video of a podiatrist painlessly debriding a corn on the bottom of the foot:
