To link iHeartRadio with Alexa from the Amazon Alexa app: 

1. From the Amazon Alexa App, tap on the More menu tab
2. Select Settings > Music & Podcasts. A list of music services available on Amazon appears.
3. Under the Services section, tap on Link New Service
4. Tap on iHeartRadio > Enable to Use

For further Amazon Alexa support visit the Amazon Support Center.