This information was provided by Tesla Service Rep.
If you are experiencing issues with your Model 3 that a simple reboot is not fixing, then you can try the steps below:
FULL POWER CYCLE
1. Make sure you vehicle is not plugged in or charging, make sure the vehicle stays parked, make sure the doors are closed, make sure the windows are up, keep your feet off the brake and acceleration, and try not to move around in your seat too much.
2. Hold in the scroll wheels on the steering wheel until the screens go blank and then release.
3. When the MCU reboots, select controls, safety and security, power the vehicle off.
4. Wait for 3 full minutes. (if the vehicle powers itself on during this time, double check that all the conditions from step 1 are met and start again).
5. Power the vehicle back by opening and closing the door.