How do I change the avatar of a user in SDDM & KDE Plasma 5?

I’m using simple desktop display manager (SDDM) & KDE Plasma 5. How do I configure the avatar picture of a non-root user, through commands (so that I can automate it)? How do I do the above in a terminal?

I can’t even find the configuration file, .ini, .conf, *rc, be it whatever. I have done kfind throughout the whole system and found nothing but the locations of those icon image files, which are of no use.