How to un-trust a computer that I have trusted with iOS 7 device, such as iPhone?
You can delete the Lockdown folder to reset the trust/un-trust status of iPhones.
Apple provides tutorials for Max OS X and Windows at: http://support.apple.com/kb/TS5335 (archived) .
If you are using Linux, the Lockdown folder is:
/var/lib/lockdown
Answered by Lucy.