Let's be frank, when a device is being pushed to its limits, it tends to get a bit warm or hot, depending on the load, and the Nintendo Switch is no exception. While there isn't an answer to this problem from Nintendo directly, the folks at Nyko have created a solution that will soon be available.
The Intercooler is an add-on airflow accessory that can be attached to your existing Switch dock. It pulls air from the outside and pushes it toward the rear of the console. Perhaps what is best about this accessory is that it has a built-in temperature monitor that will automatically turn the fan on and off when needed. The Intercooler is powered through USB, so you will need to power it using one of the internal or external USB connections located on the dock.
Speaking with Nyko, the firm stated that the Intercooler would be available for the Switch starting in August 2017 with a retail price of $29.99. While the accessory is listed on Amazon and is available for pre-order, the release date is set for November, which would seemingly be a placeholder date. If interested, Nyko will also offer other accessories for the Switch like its Swivel Grip and protective cases.