The Eye Experience update for HTC One M8 mainly focuses on the camera features, including the Live Makeup which is to smooth your skin before taking selfie. To enable and use Live Makeup on HTC One M8 camera, do as follows:
1. Make sure the Eye Experience update has already hit your device and you have installed it (To make sure, go to Settings >> About >> Software updates)
2. Open the Camera application and go to the Settings tapping the Gear icon
3. Make sure the Live Makeup option is enabled (Before opening the settings, enable the front camera. Otherwise you won't see the mentioned option)
4. Now you should see a slider at the top of the screen, which is to specify the extend of skin's smoothness as you drag it
** To disable the Live Makeup feature, just unmark the option from camera's settings