If you can access the recovery you can download update.zip (Global firmware only) and paste it in recovery drive of the device. Then go to recovery Vol Up + Power to go to recovery and flash the firmware. SP Flash tool does not work properly for Meizu devices so you shouldn't use it. If you cannot access recovery then go to a service center to get the service firmware reflashed on your device. Do not flash the Nougat updateon your device as it doesn't support it.