Open the Alexa app
Tap Devices
Select Echo & Alexa
Choose your Echo device
Tap Device Settings
Tap Factory Reset or Deregister
Confirm the reset
For Echo Dot with a microphone off button, press and hold the Action button for about 20 seconds
For Echo devices with a reset button, press and hold the reset button until the light ring turns orange, then blue
For Echo Show, swipe down from the top of the screen
Tap Settings
Tap Device Options
Tap Reset to Factory Defaults
Wait for the device to restart
Set up the device again in the Alexa app