SetXROrigin.cs

// Sets the origin mode for XR.
// Add this component somewhere in your scene.

using System.Collections.Generic;
using UnityEngine;
using UnityEngine.XR;
 
public class SetXROrigin : MonoBehaviour {

    public TrackingOriginModeFlags originMode = TrackingOriginModeFlags.Floor;

    void Start() {
        List<XRInputSubsystem> subsystems = new List<XRInputSubsystem>();
        SubsystemManager.GetInstances<XRInputSubsystem>(subsystems);

        foreach(var subsystem in subsystems) {
            subsystem.TrySetTrackingOriginMode(originMode);
        }

    }
    
}