iPhone "Trust this computer": How to re-trust
Source: http://osxdaily.com/2014/03/24/trust-this-computer-alert-ios/
- Try disconnecting/reconnecting the phone;
- If that does not work, try going to iTunes, in the Preferences, Advanced, click the “Reset Warnings” button.
Without iTunes, if unplugging and replugging does not work, switch USB ports.