You can get Alexa App in a few simple steps within minutes. Download Alexa App from play store for Android phones or apple store for iOS.
Always Make sure Your Echo device is connected to the Wifi network. You need to select the network and enter its PW. Also, learn how to set up echo dot 3rd generation.
Open the Alexa App and select the echo sub device in the lower side of the right corner for the Alexa Setup.
Here, you will need to click plus sign, in topmost of the right corner. Then choose the ‘Add Device'.
Now, click on your chosen Echo sub. And your Alexa is ready to begin.