failed migration - how to start over

Hi, I'm  new to lightroom, i've signed up to lightroom CC and wanted to migrate my Photo Library from my Mac - this worked successfully with approx 22k photos migrated and also synced to the lightroom cloud storage.

However the lightroom library file  Library.lrlibrary on my Mac HD is too large and I need to move it to an  external drive. After researching how to move the library file I shut down Lightroom app copied the Library.lrlibrary file via finder and renamed the original file on my Mac. Next step was to open Lightroom app and in preferences point the local storage towards the file on the external drive. I wasn't able to select the file and in the end it seems to have created another library which then was partially sync'd back to the cloud version but in the process I have only ended up with approx 1500 photos locally and while the cloud version has 22k photos nearly all are displayed as sync issues.

I'm really not sure how to fix this - since I have all of my original Mac Photo library intact and since i have no editing or organising work done in Lightroom there's no work that i would lose if I just delete everything and clear out all the libraries and files both local and on cloud and start over - question is what is the best way to do this and ensure a fully fresh start.

Secondly if I ever did need to move a library how should I do it properly?

Any help greatly appreciated.

Mike