it was running on High Sierra just fine, but when I took off the old files to prepare it to sell I was told to reinstall the OS. I have tried what's suggested on line and with the phone help and just now with the chat.
still can't get it. and they say the apple store downtown won't help either.
they suggest someone here might be helpful.
iMac 27″, macOS 10.13
I'm sure you've looked at this article: How to reinstall macOS - Apple Support.
If you can't reinstall macOS this way, you'll need to use another Mac to create a bootable installer: Create a bootable installer - Apple Support. You'll find the macOS installation file here: How to download and install macOS - Apple Support.
Note that, if this other Mac is too recent, it won't allow you to download macOS High Sierra. You need to use a model 2017 or older.
I'm sure you've looked at this article: How to reinstall macOS - Apple Support.
If you can't reinstall macOS this way, you'll need to use another Mac to create a bootable installer: Create a bootable installer - Apple Support. You'll find the macOS installation file here: How to download and install macOS - Apple Support.
Note that, if this other Mac is too recent, it won't allow you to download macOS High Sierra. You need to use a model 2017 or older.
i'm having difficulties reinstalling High Sierra on an old iMac
