Did you get a pre-built Atreus62 from Profetkeyboards.com with no clue how to edit and re-flash your layout? Here are the steps I took to get it working on a Mac. YMMV:

Download the QMK firmware by following the QMK quick start guide. Create your custom keymap as per the docs. Go to the Quick Start guide and install avrdude Determine the path to the keyboard by running some terminal commands. Note: when it says to put your keyboard in bootloader mode, all you have to do is get a paperclip and stick it in the hole in the back of the atreus62. You now have 8 seconds of bootloader mode. (tip: you can also activate Bootmagic) Flash your hex to the keyboard by putting it in bootloader mode and running the terminal command as shown a little farther down here. For example, in my case,

avrdude -p atmega32u4 -c avr109 -U flash:w:atreus62_mylayout.hex -P /dev/cu.usbmodem1411

That’s it! From here on, I can tweak the layout, compile the hex, and flash it.

Here’s my current layout: