Synology - DSM 7.0 Release - Plex Installation (Not Operational) Issues

Just got around to doing the upgrade. DS920+ (Intel).
I installed it following the instructions here. It went all the way through without asking for me to give access to the PlexMediaServer share to PlexMediaServer, which was a bit of a surprise. Got to the end, then told me to give access to the various media shares, so I did that.
Then I started it, and it gave me the standard wizard for a new server. So I clicked Next, thinking that I could see what it was going to do, and it would walk me through the migration. Which I’m now pretty sure was a mistake, as the current name of the Synology and the existing name of the Plex server are currently different. So instead it created a new server, with a new name, and doesn’t have access to the old server at all.

I’ve now given it access to the old Plex share, and I’ve tried uninstalling and reinstalling, but it’s still not migrated the libraries across.

What do I need to do to back things out entirely and get my libraries back?