1. If you have a custom recovery installed then you need to first install the stock recovery to install the OTA update. Here is the link for the stock recovery 1.56.720.6, CID: htc_038, HTC M8 India. LINK:"http://forum.xda-developers.com/htc-one-m8/general/htc-one-m8-stock-recovery-indian-t2848324".
2. Now flash the stock recovery using fastboot or use the Hasoon2000 All in One Kit. LINK:"http://www.hasoon2000.info/?device=One%202014%20(M8)"
3.Reboot the device and install the Update .
Hit Thanks If you find my post helpful.