IF the kernel has settable speed, it would be in whatever app is being used to control that. (You can't "cool" the CPU, the best you can do is run it slower, which produces less heat.) If the kernel you're running doesn't have speed control, you can't.
(You may have seen an app that claims to cool the CPU, but if you have take note of the developer and stay away from any apps from that developer. It's a fraudulent claim, and the app is probably stealing data from you - like logins and passwords.)