I think the instructions you were referring to were these from @egrath which I moved to a different thread:
For the record, we have a built-in eos-rollback command to do this in one step.
The error message you give above is interesting because it refers to com.endlessm.Demo.Os. Had you previously switched to the beta channel? Can you get a diagnostics file by following these instructions, and attach it here?
https://support.endlessm.com/hc/en-us/articles/208416346-How-do-I-make-a-debug-log-of-Endless-OS-