Nope... . No app can cool device... If you install such gimmick apps, that will add to more heating... . Best practice would be keeping rarely/less used apps to Deep sleep and restart device once in a period of 1-2 weeks... Charge your phone without backcover (if phone is heating while changing) ... Try not to use phone while changing... . Nothing more can be done ... 😬 Mostly it depends on the Phones OS... A module "Thermal Guardian" in Good Guardian which says to keep device temperature low (but I have not seen this to work). You can try it... But you'll have to sacrifice the device's performance... It limits processing power of device to minimise heating . It's summer season, so it's by default that phone will heat if you do heavy tasking (and if you are not in a well cooled room)
