Follow quick instructions here or check detailed RM firmware upgrade document.
which avrdude || sudo apt-get -y install avrdude
https://play.google.com/store/apps/details?id=ru.zdevs.zflasheravr
Make sure to pick one according to country/carrier. Otherwise data will not work and you'll have to configure it using sms.
Connect USBasp programmer to your laptop/mobile phone and connect the ISCP header.
Cable direction is to inside of the device, not the outside. Backup will not work, and it is electrically safe to turn the cable 180Deg.
avrdude -c usbasp -p atmega328pb -U flash:r:md_backup.hex:i
Check the output for errors and file for a reasoble size (10k+)
avrdude -c usbasp -p atmega328pb -U flash:w:md_03_v1.01_2023_09_11_cz.hex:i