Reset Echo Auto
If you want to sell the Echo Auto or use it in another car, the device has to be reset first. This is done by holding down the “Microphone off” button while pressing the “Action” button for 15 seconds.
The device will first confirm the process by lighting up from left to right in orange, which changes to a flashing light when the sequence is completed. At this point Amazon Echo Auto has forgotten all paired devices and is ready to be used in a new vehicle.
https://diysmarthomeplanet.com/echo-auto-setup/#Troubleshooting_Troubleshooting