All you need to do is put that page into its own section. For example if most pages are set to portrait orientation and you want one that’s landscape, create a new section before the landscape page and after the landscape page.
Let’s say the first part of your document is in Section 1. Now you’ve created a Section 2. Set this section to Landscape Orientation. At the bottom of the Landscape page insert a new section break. Now set the new section, Section 3, back to Portrait.
You can switch orientation as often as you like as long as you keep the sections separate.