To find the "Add Airtime" screen on your Tracfone ZTE Valet Z665C, start by unlocking your phone and accessing the main menu. Look for the "TracFone" app or icon, which is usually pre-installed on the device. Tap on it, and you should see an option for "Add Airtime" or "Add Minutes." Follow the prompts to enter your airtime card information or purchase airtime as needed.