Thanks to DannyC on the Rivian Forum for this:
Sleep Reset
Rivian must be unplugged from charger, nothing plugged into any USB ports, Inverter off, all seatbelts unbuckled, no one in the vehicle. Then lock and walk away for at least 30 minutes.
Infotainment Reset
Hold the far left and far right buttons on the steering wheel for about 15 seconds. This fixes issues having to do with the screens, hotspots, Alexa not working, glitchy navigation, etc.
Full Reset
Hold the far left button on the steering wheel and the emergency flasher button for about 15 seconds. The entire computer will restart.
According to Rivian support DO NOT RESET AGAIN FOR AT LEAST 1 HOUR after this procedure. There are multiple systems that may take a bit longer to fully come up after this reset.
