When creating some tests in Nelio A/B Testing, you need to indicate which is the original page/post you want to put under test. To do so, you have a selection list where you can see some of your pages/posts:
As you can see, the list only show a partial selection of your posts or pages. However, there is the chance to find the specific post and page that you want to test by writing its title (or some keywords) into the selector. When writing some words, the results in the list will dynamically change showing the entries that are relevant.
Note that you can also search posts and pages by their URLs or by their IDs. Type the URL of a page or its ID directly in the search field to get new results.