When flashing the first time using handedness by EEPROM, use the [QMK guide for that topic](https://docs.qmk.fm/#/feature_split_keyboard?id=handedness-by-eeprom).
See the [build environment setup](https://docs.qmk.fm/#/getting_started_build_tools) and the [make instructions](https://docs.qmk.fm/#/getting_started_make_guide) for more information. Brand new to QMK? Start with our [Complete Newbs Guide](https://docs.qmk.fm/#/newbs).