Accessory maker Dobe has created a cooling fan specifically built for Nintendo Switch.
The cooling fan is powered by USB, so you can directly connect it to the Nintendo Switch Dock for power. The fan is attached to the back of the Dock, the closest it can get to the Nintendo Switch console.
You can control the fan’s speed too – there’s a normal option and Turbo option (in case you are afraid of your Switch heating up too much). Buy the cooling fan for Nintendo Switch from Amazon here.