Power off the HTC 10 completely. Then keep the power on/off button pressed to reboot the smartphone. Once the screen is activated and displays the HTC start logo, immediately hold the volume quieter button. Keep it pressed until the sim-pin is queried. At the bottom left you should now find a field with “Safe Mode“.
HTC One A9 Android smartphone. Announced Sep 2015. Features 5.0″ display, Snapdragon 617 chipset, 13 MP primary camera, 4 MP front camera, 2150 mAh battery, 32 GB storage, 3 GB RAM, Corning
BC2M7v6.