how do I restore my Mac from a backup in iCloud?

On a Mac, you can restore from a Time Machine backup, but not from an iCloud backup like you can on a iPhone. You can still use iCloud to sync photos, messages, your Documents a Desktop folders, and any files saved in iCloud Drive but the OS and Application sizes are too large for normal backups. To get hourly backups on a Mac, you will need use Time Machine. This will require an external drive that can be connected with a cable or wirelessly. For more information on using Time Machine and iCloud for saving files on a Mac, here is a support article:

How to back up your Mac - Official Apple Support

Mac Jim ID is correct... iCloud is not a true backup solution for the Macintosh computer. iCloud excels at provide access to some of your files and photos across different devices no matter where you are. iCloud can be used to backup the iPhone, iPad and iPod, but not the Mac.

You should have been advised by the tech to do a real backup of your Mac with Time Machine before the service was performed, for exactly this reason.

iCloud - Official Apple Support

Back up your Mac with Time Machine - Apple Support

Restore your Mac from a backup - Apple Support

When you sign in with the AppleID under which you placed data in iCloud, that data will be loaded into your iCloud Drive folder.