Simply make or copy the shortcut to CCleaner to the desktop.
Right click and go to Properties.
The Target will read "C:\Program Files\CCleaner\CCleaner.exe".
To make it run automatically, make the target read this: "C:\Program Files\CCleaner\CCleaner.exe" /AUTO
Next, move the shortcut into the Start menu's Startup folder.
This has been suggested. Still waiting to see where this is going.
It would be safe to clean, as backups are made.
In CCleaner look to Options, then click Cookies.