Basically you'll need to go from Kochi to Kumarakom, n then double back and got to Allepy. See the google map: https://goo.gl/maps/hXetgMDsc7o Kochi to Kumarakom route:
Airport - ( 4 Kms) to Athani airport junction road - Reach Edappally junction ( and Lullu mall junction_ . take left -Vytilla junction - Aroor toll - Aroor junction - Thuravoor - Cherthala - take left from where the byepass starts ( Karthayayani hotel ) - reach court junction - drive straight 800 m - take right drive 500 meters - take left from the junction ahead ( this is just east of KSRTC bus station cherthala) - drive to Thannermukkom - cross Thennermukkom bridge cum shutter over vembanad lake - drive till bund road junction - take right - drive past kaipuzha muttu bridge - cheepunkal bridge - kavanattinkara bridge ( you see Taj vivanta to your right - drive till kumarakom boat jetty and bridge - 100 meters from there take right to Zuri Hope this helps! Happy journey.