Keychron regular K series are not supported by QMK/VIA yet, only the Q series, V series, and K Pro series are QMK/VIA enabled. So your K6 does not have a keymap/JSON file nor is detectable by VIA.
If you have a regular K series model and want to program it, you can use Karabiner for macOS, or Sharpkeys, Keytweak, Keymapper, and AutoHotkey for Windows.