Rona is correct. The fan trim pot controls the exhaust fan. The convection fan is governed by the thermocuple reading. You can use the computer to change how the exhaust fan responds to the thermocouple. It is explained here, but it's not all that intuitive.
forum.iburncorn.com/wiki/index.php/Bixby...vection_Fan_Settings
If you tell us your present settings (on your Bixcheck Fuel table), and tell us what you want to accomplish (e.g., faster speed at lower temperatures?), then we can advise you what to set them at. Personally, I like a high fan speed to move the heat, so my settings presently are:
TC for 25% fan: 10
TC for 100% fan: 140
This means that for a thermocouple (TC) reading of 10, my fan will run at 25% rated speed. By the time the TC reaches a reading of 140, the fan is running at max.
Does this help?