Hello cindi203,
While you can configure the Siri Remote to turn your TV on or off, change the input to your Apple TV, and even control the volume, there isn't a volume control built into Apple TV. Your Apple TV, like newer headphones or speakers, doesn't have volume controls built in, because they rely on the device playing the media to control the volume. You can learn more about controlling your TV volume here: Control your TV and volume with the Siri Remote - Apple Support
That said there are some steps we can take to identify the source of the problem. The first thing to try would be to connect your Apple TV to different TV using a different cable. If the issue continues, it may be related to your Apple TV and hardware service may be needed.
If it doesn't continue, it issue would be related to your cable or TV. You can further narrow the issue down, by trying a different HDMI port on your TV.
Thanks.