Firstly, turn off the power control of the baseboard heater and cool it. Then take off the cover and remove the dirt particles present inside the heater. You can use a small vacuum cleaner to clean the inside of the baseboard heater. You may also use different cleaners like pressure cleaner but with protection to avoid damaging the floor or the inside of the heater. In the end, wipe down the cover before putting it back and covering the heater.