I've read some posts that mention Config.template.h, but I couldn't find it in the game's files. So please help me find where I can change the game's simulation area. I am currently playing at the newest public version of 99.3.384
SimulationConfig.h is what you want, not Config.template.h, but changing it requires modifying the source code and recompiling TPT, see Powder Toy Development Help for that. You can use The Resizable Toy mod instead