To set your default OpenXR runtime follow the step by step guide that corresponds with the VR headset of your choice.
Oculus

- Open your Oculus software
- Navigate to Settings -> General
- Click the ‘Set Oculus as active’ button to choose Oculus as your active OpenXR runtime
- Depending on your Oculus software version this option can be under ‘General’
Windows Mixed Reality

- Start the Mixed Reality Portal software
- Click the ‘Fix it’ button on the notification banner at the top of the screen. This will set Windows mixed reality as your default OpenXR runtime.
HTC

- Start Vive Console
- If your runtime is not set to Vive a popup will appear
- Select yes to set Vive as the default OpenXR Runtime
SteamVR

- Open SteamVR
- Open the settings from the hamburger menu
- Click Show ‘Advanced Settings’ at the bottom left corner
- Select the Developer tab
- Press ‘Set SteamVR as OpenXR runtime’