Use device manager to find COM port that ArduinoISP uses.
Download Blinky sample project.
platformio.ini file:
[env:arduinoisp] framework = arduino platform = atmelavr board = atmega328pb board_build.mcu = atmega328pb board_build.f_cpu = 16000000L board_fuses.lfuse = 0xFF board_fuses.hfuse = 0xD6 board_fuses.efuse = 0xFD upload_protocol = custom upload_port = COM5 upload_speed = 19200 upload_flags = -c stk500v1 -C ${platformio.packages_dir}/tool-avrdude/avrdude.conf -p $BOARD_MCU -P $UPLOAD_PORT -b $UPLOAD_SPEED -e upload_command = avrdude $UPLOAD_FLAGS -U flash:w:$SOURCE:i