The cable end with the purple label and a dot plugs into the USB-C port on the left side of the headset. Do not connect the cable to the right-side USB-C port, which is only for accessories such as the Audio Strap.
The cable end with the orange label and a D-shaped plug connects to the Link Box, which has a matching D-shaped slot. If you connect this D-shaped plug into the headset, you may see the LED turn on, but the headset will not operate.
This means your headset cannot see the SteamVR Base Stations, which are required for the headset to operate. Ensure your SteamVR Base Stations are turned on and facing the Beyond, and follow the base-station setup guide to configure them correctly.
Open the Bigscreen Beyond Utility, which is installed via Steam, and set your preferred refresh rate there.
The headset should now function as expected.