Consult documentation (Installation Instructions) for proper instruction. Follow this step only if you lack official documentation.

Each oven is secured to wall by two screws, one through each side mounting flange. Remove.

Set aside racks and pans and other weight.

Find something to use as a stand/pedestal/base for your oven. Use original shipping base and shipping feet if you have them. If you lack original documentation, then probably you lack shipping material, so you can use dimensional lumber or a shelf plank.

Pull out oven, set it on a temporary stand, orient it so you have full access to its rear.