Hi DTH1956,
I see your issue above.
You will select the Macintosh HD, and make sure this information matches:
Name: Macintosh HD
Format: OS X Extended (Journaled) or Mac OS X Extended (Journaled)
However, please be aware that when you do this, all your data will be erased! This action cannot be undone! Make sure your are comfortable with where your data is stored besides the Mac. You can use Time Machine, iCloud, or an external hard drive. See this article How to back up your Mac - Official Apple Support
After you erase, let's reinstall macOS.
- Quit Disk Utility.
- Open the macOS / OS X Installer.
- Follow the on-screen instructions and select Macintosh HD as your disk to install to.
- Let the process finish, don’t restart, sleep, or shut down your Mac. Also don’t disconnect from WiFi.
- Let the process finish; then setup your Mac, and restore your data. For iCloud data, sign into your Apple ID and download data from iCloud. For Time Machine backup and restoring, see this guide: https://support.apple.com/en-us/HT203981. If you copy and pasted your data to an external hard drive, copy and paste the data back.
Hope this helps!
Cheers,
Jack