Just reformatted my iMac, now it won’t recognize external drive

I have a 2010 27" iMac. The display went on me last week, so I took it in to get repaired. The tech corrupted my OS, so he had to reinstall the OS. I told him that it was fine because I had confirmed my Time Machine backups were in place on my external drive before taking it in. I got my computer back today, but doesn’t appear on my desktop or when I browse to User’s iMac. It shows up when I run diskutil list in Terminal and in the System Information utility under USB. It shows up in Disk Utility. When I try to verify the disk, it tells me to repair it. When I try to repair the disk, it tells me it can’t be repaired and that I should back up my files, reformat the disk, then restore the backups.

Is this my only option? If not, what else can I try? It workd perfectly fine the last time it was connected to my computer and had finished doing a Time Machine backup right before I disconnected it. If this is my only option, how to I get the files off of it?

It is an Acer AH263. It has no external power supply, and the USB port on the drive is proprietary.

I have connected the drive to a MacBook, and it doesn’t appear on there either.

Thanks for your help.