@Flox Hello again.
I think what you are looking for is:
/opt/rockstor/bin/delete-rockon
Delete metadata, containers and images of a Rock-on
Usage: /opt/rockstor/bin/delete-rockon <rockon name>
ie an installed (built) system has the above convenience wrapper that sets up the required environment for the script. And with no parameters give it outputs the above ‘guide’ as to it’s use.
Hope that helps. You may have to play with getting the exact Rock-on name but pretty sure it’s the displayed name.
Also it looks like you are several versions of Rockstor behind, I haven’t noticed any issues with the interim versions re updates so you might like to upgrade to the latest as 3.9.2-11 was 3 months ago now.