It is a SETTING in the COALTROL, that's why they posted in this section. If you don't have one, you wouldn't know.
it is called MANUAL FAN (MANFAN) Override. The fan speeds are normally Automatic based feed rate, as the feed rate increases, so does the fan speed.
BUT, sometimes, you just want a little more heat before the stove gets cranking. So, you can control the speed (0-99%) manually.