Where do I turn off the auto reboot at 2 AM?
Ccleaner doesn't have a reboot feature at all. Maybe explain your problem a little more. Do you have ccleaner set to run at 2AM?
While it can't reboot your PC it can shutdown your PC if you have any shortcuts or tasks with the /shutdown parameter it in.
The command line parameters:
https://www.piriform.com/docs/ccleaner/advanced-usage/command-line-parameters