You may use the Export feature to define Page orientation. Kindly follow the below mentioned steps:
1. Open your MATLAB file as a Live Script.
2. From Home tab in toolstrip, Click "Export"
3. From export dialog box, Click "Show more".
4. Set "Page Size" and "Page Orientation" as per requirement.
For more details regarding the export options, kindly follow this documentation page:
Hope this helps!