After building your DOTS module and having it checked, you can start to flash the microcontroller with the firmware. Install avrdude on your operating system. I am using a Mac with an MRVISP MKII to flash my modules. I had troubles using USBasp flash devices.
Connect the ICSP pin header to the device, ensuring correct orientation by checking the pinout diagram. Do not connect the power header to a Eurorack power supply and the ICSP at the same time.
The repository uses PlatformIO to manage environments. Choose the device's environment, build the code, hit burn Bootloader and then try to upload it to the device. This part could work right away or may require some troubleshooting. If the device signature is empty (0x000000), check for connection issues and try another cable. Do not move the device during this process. If you have just installed VSCode with avrdude and PlatformIO, try rebooting the system.
The release files include also a already compiled .hex file. You can use avrdude to flash the firmware. The command is:
avrdude -c avrispmkII -p m328p -P usb -U flash:w:{{path-to-firmware}}/firmware.hex
If you are using the Arduino IDE, you may need to install the ATmega328P board.