Just press the lever on average meter for 2 seconds. It will reset and give you real milage. It will show abnormal average only during first few kilometres and then will settle on real average.
E.g. if you reset it during coming down a slope with no for on accelerator, it may even go to 70-80 km/ltr. Inversely if you reset it during a traffic light it will show zero ltr/hr. Hope you understand the story