The suggested troubleshooting steps didn't work to recover my Mac...I need it back to Mojave...It's been upgraded to Catalina
How can I downgrade my Mac back to Mojave? I cant use Catalina for my work
iMac 21.5" 4K, macOS 10.15
If you have a TIme Machine backup you can revert to Mojave.
Restore your Mac from a backup - Apple Support
Otherwise, you'll need to erase the hard drive an reinstall Mojave. This will erase all your data.
