I've built my own ESP32C3 board; how do I start using it with PlatformIO?

I am not sure what files I need to change or add in order for my new ESP32C3 file gets listed as a possible board for me to use for development.

Any help would be appreciated.

See Custom Embedded Boards — PlatformIO latest documentation.

As the most simple test, create a new ESP32 + Arduino project, then in that project create a boards folder and create new file myboard.json, where myboard can be named anything you want. Content-wise, try and use platform-espressif32/esp32s3box.json at develop · platformio/platform-espressif32 · GitHub or platform-espressif32/esp32-s3-devkitc-1.json at develop · platformio/platform-espressif32 · GitHub with the modifications for your specific board (flash size, flash mode, PSRAM, …)