You must be familiar with the pop ups “Trust this Computer?” with “trust” and “don't trust” options, while connecting an iPhone, iPad or iPod touch. If you choose to tap on “Trust”, it will allow the computer access to the device.
Now, given how easy it is to accidentally tap on “Don't Trust” which can be reversed, it's a little frustrating that there isn't an obvious way to “UnTrust” a computer that you accidentally trusted from the iPhone or iPad too, right? Well it turns out you can undo the “Trust” selection when an iOS device is connected to a computer.
However, following this setting youll end up resetting the “Trust this computer?” alert on the specific iOS device for all computers it has connected to. Every time you connect the iPhone, iPad, or iPod touch to any computer, this simply results in the familiar “trust” or “don't trust” choice again, even if you trusted that computer a long time ago. This is not much of a bother but it is worth pointing out. Additionally, one will reset all other privacy and location settings customized on the device, so be ready to make some customization again to those settings.
How to Reset the “Trust This Computer” Alert and UnTrust All Computers from iPhone and iPad
Step #1. Tap on Settings on the iPhone/iPad → Tap on General.
Step #2. Scroll down and tap on “Reset” → Tap on “Reset Location & Privacy”, enter the devices passcode, and confirm that you wish to reset all location and privacy settings on the iOS device.
To trigger the “Trust This Computer” alert on the iOS device again with a computer, you can simply plug it back into a Mac or Windows PC with a USB connection and you'll see the familiar alert screen popping up again, allowing you to select either choice.
Now you can always choose to make a “mistake” ;) and still secure your data.