To add the Xfinity app to your Fire TV, please follow the steps below:
1.  Press the voice button on your Alexa Voice Remote.
2. Select the Xfinity app.
3. Select 
Get or the shopping cart icon to download the app.
If you can not find the app, please check for the TV update.
1. Select 
Settings on your Fire TV.
2. Choose 
My Fire TV.
3. Select 
About.
4. Choose 
Check for System Update.