If you want it on while driving, you have follow the steps below.
- Make sure your Personal Hotspot is enabled on the iPhone (Settings > Personal Hotspot > Allow Others to Join should be green)
- Put the car in drive (or reverse) but don't move - Hold usually does the trick. DO NOT DO THIS WHILE DRIVING
- Tap the LTE bars at the top of the Tesla screen. Select WiFi Settings
- Tap to turn on WiFi. It will ask for your WiFi info on this screen, but I have found it easier to just close the window.
- Tap the same place on the screen as step 3 - it should be a WiFi symbol, but it may be the LTE bars for a few seconds.
- Select your phone from the menu. It will ask for the WiFi password the first time (and sometimes on subsequent attempts)
Since I can't get a WiFi signal to my garage, this is what I do every time there is an update.