An antivirus will not stop your phone from overheating. When you use the phone the cpu has to work and that generates heat. Proper cooling in a phone should stop it getting too hot. Are you in the USA, Canada or China? Or are you from somewhere else? The Snapdragon chip from those areas tends to run cooler than the Exynos chip in the international version. I have an Exynos based S10+ and my phone doesn't tend to run too hot, but I know a lot of people complain about it.