I found the UI Configurator online (https://keyboard-configurator.massdrop.com/ext/ergodox) and made a custom keymap, and downloaded the .hex file. But the instruction optimistically say "load onto the Ergodox". How? I am running Windows 10. Do I really need to install Cygwin? What is the simplest way to change the keymap?
HazerThat configurator is for the original ergodox, not the Infinity. Please follow the instructions here, and keep in mind that you'll want to flash each side (though later you can flash only the master side, barring critical fixes):
https://input.club/configurator-setup/