Audio mixer?

[The1nonly1]

I have my steelseries arctis 5 headset plugged into my PC via USB A for sound. I also have a second display that I either use as a monitor or for watching streaming services from a firestick on. This second monitor has sound but also has a 3.5mm jack for headphones. How can I get sound from both PC and the second display through my steelseries arctis 5 headset at the same time so I can hear both? Is there hardware that will allow this? I know hardly anything about sound so help is appreciated. Thanks.

 

[The1nonly1]

To add onto this, is it possible via software if I use a 3.5mm cable from the display to my PC via the line in port? I think I have steel series software already that has a mixer.

 

[The1nonly1]

Thanks, I'll give the software route a go first. It's steelseries sonar which my headset and mic (not steelseries) go through an has the control for aux so sould work. I've ordered a 3.5mm cable top try first.