The first time you run VirZOOM Arcade, after your bike is powered on and your VR headset tracked, you will be asked to recenter your VR headset.
Hold the L (left) and R (right) trigger buttons while you are seated on the bike and looking forward. This allows the VR system to detect your head position and the direction you're leaning, which are used for steering and menu navigation in the game. If you ever need to recenter during a game, hold both triggers for a few seconds. This will allow you to repeat that process on the fly (say, if you need to move your bike across the room without quitting the game).
The game then asks you to lean left and right, like the blue figure shows, to make sure you have full range of motion.