I also flashed mine with micropython. To get it back to the factory program that came installed, I connected it to the Arduino IDE, selected Tools > Board: M5Stack-Core-ESP32. Next I opened: File > Examples > M5Stack > Basics > FactoryTest. Upload that to the m5stack and you should be back to the factory program.
If you don't have the M5Stack custom libraries, you can install it from Sketch > Include Library > Manage Libraries... Type m5stack in the filter box, select the result, and install the latest version.