You’ll need, somewhat obviously, a HDMI to component converter, or a HDMI to (ideally RGB if your TV supports it) SCART block.
You’ve got two problems here though. The first is that HDMI is digital, and component (and SCART) is analogue, so some sort of converter will be necessary rather than being a simple cable.
The second, and potentially bigger, issue is that HDMI is ‘clever’ and requires communication between the two devices. In part this is copy protection; if a video player can’t establish that it’s talking to a legitimate playback device it may fail. What we’re describing here is essentially a device which can bypass copy protection. Whether this affects the Xbox or not I’m not sure; if I were to guess I’d hazard that it’ll fail for commercial video playback (eg Netflix) at least, if it works at all.
What this means in practice is that any solution is either going to be expensive, a bit crap, or just not work. I’d guess that most HDMI / component converters will convert from component to HDMI rather than what you need which is the other way around.
If I were you, I’d either look to replacing the TV (which there’s an argument for anyway, you might as well have bought a 360 as hook a One through an ancient TV), or use a Windows 10 PC as a remote screen.