Developers behind HTC One M9 are working very hard in bringing custom ROMs and the first thing required before flashing any kind of modification is a custom firmware is a TWRP. It allows the user to flash not only custom firmware on to the HTC One M9 but also other mods such as custom kernel mod, root and so on.
So there you have it – the TWRP for HTC One M9. I prefer it over CWM a k a clock work mod as it allows touch screen interaction and supports landscape mode – both of which are not supported by CWM. You can download TWRP from following link. To flash it, use ODIN on your computer and put your phone in download mode.