OSX Daily had posted a tips to untrust your device when you accidentally tap on a computer that you shouldn’t trust. But the trick will untrust all devices that you already pick as trust too. But it does not matter because you can always choose to trust again.
Step by step to untrust all computers in iOS (iPod Touch, iPhone and iPad)
- Open Settings
- Choose General
- Choose Reset
- Scroll down to Reset Location & Privacy and tap on it
- You are done