There is no flight mode option on the Assure watch phone. You can simply power off the watch when going on a flight by gently pressing a pin into the reset pinhole located just above the the USB charging port.
Or you can click on Watch Settings in the App and select Power of the watch remotely. You can set it to automatically power back on at a set time. Alternatively when you reach your destination you can power back on the watch and wait a couple of minutes for the watch to activate. Remember if you have changed time zones, you can update the watch time in watch settings.