How to downgrade Nougat 7.0 to Marshmallow 6.0 for Zenfone3max ?

Hi,


I've downloaded an upgrade for mu ASUS ZENFONE 3 MAX (ZC520TL), and now, there's a lot of problems : facebook, twitter, google application doesn't work anymore (applications close when i try to open it).
How can i downgrade please ?

sad to say, as of now there is no available downgrade firmware for that.

I want to downgrade Android version 6.0..