Local Online Mode is an automatic feature built into Synapse designed to keep your scanning environment stable during occasional internet outages. You do not need to do anything to turn this feature on or to restore itself to standard online mode.
NOTE: During onboarding or after switching from offline mode, be sure to remove previously connected WiFi networks that are in range of your iPad and INSiGHT Bridge. iPads switch networks automatically based on signal strength and it will interrupt your scanning experience. To forget previous networks on your iPad, go to Settings > WiFi > Choose Network > Forget This Network.