Cropping is a fundamental and basic tool of any photo editing program. And while Lightroom has a built-in cropping tool available, it’s not super obvious on how to change orientations. To do so, start by using the crop tool and then click the X key on your keyboard. If you’re cropping an image that’s originally horizontal, this will change the orientation to vertical, and vice versa.
To change the crop orientation back to the way it was, click the X key again, or click the Esc key to exit out of the crop tool and not have your crop applied.