Adding a fan to improve air circulation in this filament drier is a common mod. Here is my variation.
The first step is to source a voltage for the fan. The PCB already has unpopulated locations for fan components. I added a connector, diode D2 and a 30V n-channel Mosfet Q1. The gate of Q1 is connected to pin 16 of the MCU. This means the fan will come on when the LCD backlight is on.
I fixed a 4010 24V fan behind the display with hot glue and cut a small opening in the hot plate to let the air circulate. I also wired up an MP1584 buck converter module to allow control of the fan voltage, speed and noise.
And here are the temperature profiles inside the unit measured at the top of a roll of filament. The first run is with the fan set to 12V. The second with no fan.