How the reset Quartz64-b onboard memory (emmc)

[beepy]

Hello,
Any general help or understanding what is going on here, much appreciated....

I have the Quartz64-b handy.

( [not really relevant]... I tried installing Manjaro's img and it worked 100pc okay.
Then tried https://github.com/jaredmcneill/quartz64_uefi and finally got it's boot menu showing.  - okay)

I then installed ArchLinux Arm and THAT worked - but the onboard ethernet was down (I suspect it's kernel build re a setting should fix it) 
  -did a full pacman -Syu  (and installed a few pkgs)

-I THEN tried plebian and dietPi OS (on a DIFFERENT sdcard)
 and they BOTH cannot boot now (also the Manjaro), complaining the root filesystem is missing.

Has ArchLinux ARM loaded the onboard eMMC (or NRAM etc) with its own /boot/extlinux/extlinux.conf settings?
As -its- root label is 'rootfs' while the others are 'root'

please note: 2 different sdcards, and a clean install of Manjaro / Plebian /DietPi.

Yes, I can provide boot logs, but if anyone knows how to re-flash/re format the onboard eMMC much appreciated.
I cannot see it in /dev, and its not mounted any where

Thank you.