You would have to make sure the AppEUI and AppKey are exactly as they were before since there’s no way to change them on the device. I expect the AppKey will be different each time it’s generated, but there seems to be an option to override it and paste in the old AppKey for that device.
Also make sure the sensor is properly reset to trigger a join. Setting the device to standby mode and back doesn’t trigger a join if it thinks it’s already joined. Using the magnet for 20 seconds will hardware reset it, triggering a join.