You can force close the CBS app on your Amazon Fire device with these steps:

On your Fire TV
1. From the Amazon Fire TV Home Screen, select “Settings.”
2. Select “Applications”, then select “Manage Installed Applications.”
3. Click on the CBS app.
4. Click on “Force Stop.”

Relaunch the CBS app!

On your Amazon Kindle
1. Swipe down from the top of the screen of your Kindle Fire HD to reveal the menu. Tap Settings. 
2. Tap Apps & Games. 
3. Tap Manage All Applications.  
4. Tap the CBS app, and Force Stop.

Relaunch the CBS app!