ZBT-WE1026: HowTo flash openwrt?

Trying to flash official openwrt (target: ZBT-WE826) to a factory new WE1026 does not work, when trying to use GUI, similar to LuCi.
Any suggestion, what to do ?

Note: No ssh provided on this WE1026

Why don't you use the official WE1026 image on your WE1026?

Cause I haven't found any. The WE1026 is different to the WE1026-5G.