Help with marhsmallow multi window feature on asus zenfone 2 (ze551ml)

HI THERE FIRST TIME XDA USER HERE. I HAVE READ ABOUT THE MULTI WINDOW FEATURE FOR MARSHMALLOW USERS HERE. THOUGH CAN YOU HELP ME TO ENABLE THIS ON MY ZENFONE 2 ZE551ML (NOROOT)? I TRIED IT AND AT FIRST WORKS FINE THOUGH AFTER I AM ON BOOTLOAD IT JUST STOPS THERE NOTHING MORE..:confused::confused::confused:

TIA IN ADVANCE! <3 :good::highfive::fingers-crossed:

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