Not a very detailed description of your problem. I'd plug the Fire TV 4K directly into your TV first to see if that works.
To hook a receiver to your TV you'll need an HDMI cable between the two in the ports designed just for that. Then you'll need to plug the Fire TV 4K into another HDMI port on your receiver. Then on both the TV and receiver you need to specify which port you are using. Presto!
If you did all this, what is not working? Picture? Sound? Both? Make sure you turn up volume on the receiver in case it is set to zero.