Recovery Mode HTC One M9
First of all, hold down the Power button, until your device is off.
Afterwards press and hold Volume Down + Power key for a few seconds.
You should release held keys as soon as the new menu appears on the screen.
Afterwards use the Volume keys to select option “Reboot to Bootloader“, and press Power button to confirm.
Then press Volume Down to select option “Reboot to Recovery Mode“, and press Power button to confirm.
As soon as the phone with the exclamation point appears on the screen hold down Power key.
While holding down the Power button press and release Volume Up key.
Well done! Then you will see menu of Recovery mode
You can use Volume buttons to scroll, and select options with Power button