Unplug the drill or remove the battery
Set the drill to reverse
Hold the chuck firmly
Open the chuck jaws if needed
Turn the chuck counterclockwise by hand
Use the chuck key if your drill has one
Grip the chuck with a cloth or glove for better hold
Tap the chuck lightly if it is stuck
Apply penetrating oil if the chuck is jammed
Use pliers on the chuck only if necessary
Remove the drill bit once the chuck loosens
Tighten the chuck again after removing the bit