The ATmega328PB on this board is programmed using the standard Arduino IDE.

To compile code for this specific microcontroller, you’ll first need to install the MiniCore board package, which adds support for the ATmega328PB and similar chips.

Once MiniCore is installed, burn the bootloader using the appropriate settings—after that, you're ready to upload the firmware as you would with any Arduino project.

See the included source code for details.