Help in downgrading my Honor 6 from Android M to L.

Hi there, I'm new here so bear with me if I make any mistakes. So I have installed OTA Marshmallow update on my Honor 6 few days back. Now it only works when it's connected to a power source. When I remove the charger, I can just make calls, if I try to open anything, the phone just shuts down and doesn't power on unless connected to charger.
I want to downgrade to previous version Lollipop. Any guide on how to do it?
Specs:
Honor 6 H60- L04
Build: H60- L04C675B831
Android Version: 6.0
EMUI 4.0

Thanks for any help.