Q: This didn't work and now Photo now can't access the library it used to access. How do I reverse these Terminal commands?

The advice in this article accurately describes a problem I was having getting my 2013 MBP running Photo to import my old iPhoto library from a back up. I belatedly backed up my old iMac running Mavericks, which I'm gradually decommissioning, using Time Machine. When trying to import the back up of my iPhoto library into Photo I got the message "An error occurred while repairing permissions - Photos was unable to repair permissions on your library". In an attempt to rectify this i followed the instructions in this article. It didn't work. Now when I open Photo it can't/doesn't access the existing Photo library on my MBP that it previously accessed. Put basically - How do I reverse the above Terminal commands and get back to square one? Any advice would be REALLY gratefully received.