1.Unlock the bootloader if not already unlocked
(Make sure to set up device with phone after unlocking bootloader otherwise no boot!)

adb reboot bootloader
fastboot oem unlock
2.flash TWRP for your device (REQUIRES read only access to system!,

fastboot flash recovery recoveryname.img
3.Download special SuperSU with busybox by Jrummy included
and move it to watch with adb push to /sdcard while TWRP is booted and then install as normal zip

adb push nameofzip.zip /sdcard/

4.IGNORE SYSTEM NOT INSTALLED Boot watch to system and open Busybox app and click install