I need help with my QoS settings (Centurylink)

I have a device on my wireless network (centurylink) taking up massive amounts of my internet speed. I want to limit the service for this device.

I have a few questions.
Which DSCP Classification should I assign to the device to give it the absolute minimum bandwidth? (CS1-7?, AF ?)

Is the device the source or destination device?

Where can I find my destination netmask and port range be?

Thank you