Fire up https://config.qmk.fm/#/redox/rev1/LAYOUT and load in the json file.
Build firmware in the app, download and extract the source zip.
Build and flash with
make redox/rev1:ian_qwerty:avrdude
If you have to, manual flashing with a hex image looks like this:
avrdude -p atmega32u4 -P $(PORT) -c avr109 -U flash:w:$(HEXFILE).hex
e.g.
avrdude -p atmega32u4 -P /dev/cu.usbmodem14501 -c avr109 -U flash:w:redox_rev1_default_9ea0103.hex