1.) The first step is to flash the Vial hex onto the pro micro. Open QMK toolbox and click "Open", then navigate to the "yeehaw_vial.hex" you downloaded above. Next, make sure atmega32u4 is selected from the dropdown in the Microcontroller section. Now plug your Yeehaw into the computer, and press the reset button on the back of the PCB. Click "Flash", and QMK toolbox will flash the hex file onto the pro micro. If the flash is successful, you should get a message saying, "avrdude.exe: X bytes of flash verified".