You can only restore the whole bookmarks file to a previous state. It's not possible to restore individual bookmarks.
Please triple-click anywhere in the line below on this page to select it, then copy it to the Clipboard by pressing the key combination command-C:
~/Library/Safari
Quit Safari.
Select
Go ▹ Go to Folder
from the Finder menu bar. Paste into the text box that opens by pressing command-V, then press return.
A folder window should open. Restore the file named "Bookmarks.plist" in that folder from a backup that predates the unwanted changes.
If you don't have such a backup, but the bookmarks are still present on an iOS device (iPhone, iPad, or iPod Touch) that synchronizes with iCloud, then see below.
Back up your iOS devices. Turn off iCloud synchronization of Safari on all devices except one of those. Quit Safari and delete the bookmarks file on the Mac, then enable Safari sync on it. Launch Safari. The bookmarks should sync from the iOS device.