Someone should create a case that make you remove your phone's back plate and cool the back of it, directly on the battery or the microsd/microsim card metal piece(holder) which gets so hot sometimes that it causes burns.

Literally just put your phone in a fridge and wait for 30 seconds or more.

Battery getting hot

I don't recommend using apps to cool down your phone. They themselves run in the background and consume lot of processing power plus battery life.