You can reset your view by setting the floor of the guardian when you begin your VR session, or by holding the Oculus button and right trigger at the same time.
Typically, when the height of your view is incorrect, you can hold the Oculus button and right trigger until a circular loading bar appears in front of you. When the loading bar completes, that is where the menu and shield height will appear.
For more details, please see the Meta Support Guide on resetting your headset view here.