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.