I did do a backup. I have played with the customizer backup again and I guess I used the wrong method to use the backup – I used the ‘upload backup’
button (because I had downloaded it I thought I needed to upload it). But then I tried the ‘revert to this backup’ button and that did work. For some reason I didn’t notice that button the first time.
Thank-you for your quick reply. I am all set now.