player.cs

void Update ()
{
    if (Input.touchCount > 0 && Input.GetTouch(0).phase == TouchPhase.Began)
    {
        HandleTouch();
    }
}

void HandleTouch()
{
    Touch touch = Input.GetTouch(0);
    if(touch.phase == TouchPhase.Moved)
    {
        Vector3 cameraRelativeDeltaPosition = screenXY2CameraXZ(touch.deltaPosition);
        playerOffset.x = playerOffset.x - cameraRelativeDeltaPosition.x;
        playerOffset.z = playerOffset.z - cameraRelativeDeltaPosition.z;
    }
}