My Start-Up disc on my 2011 iMac [High Sierra] is not repairable with Disc Utility. I made a copy of my Start-up disc from Time Machine & stored it on an External Hard Drive. I load my Start-up OS from the External Hard Drive
However, the External Hard Drive is currently showing some damage (-It can not be repaired with Disc Utility First-Aid.
I have a new 2019 iMac desktop still in the box. I am trying to "REPAIR" my current problems before I use Migration Assistant to transfer all my data to my new computer.
Please tell me different methods to repair my Mac. OS Start-Up disc.
(N.B. I do not have a complete copy of my Documents & Downloads stored in my iCloud)