Make sure that your Echo / Echo Dot were connected to a Wi-Fi network, only Echo 2nd Generation support this function.
Please refer to the below link to setup your Echo/ Echo Dot.
Step1: Go to https://alexa.amazon.com from Safari, Chrome, Firefox, Microsoft Edge, or Internet Explorer (10 or higher) on your Wi-Fi enabled computer, then select Settings and click your Echo/ Echo Dot’s name.
Step2: Click Bluetooth.
Step3: Set the speaker into paring mode, and click ‘Pair a new Device’ on your PC.
Step4: Click ‘Torpedo Plus’ .