How to edit items outside of breakpoint view?

I’m using Relume’s Testimonial 27 layout. This has five or six sections in order to enter your testimonials.

On desktop, you can see two of them in the viewport. In the navigator, you can see the next one that’s out of view of the editor (along with the rest of them).

Do you need to create it as a CMS collection in order to populate and edit them?

Edit - I’ll leave this up for other beginners like me who might miss it. There’s a slider link that can be clicked that then brings the text box into the view port to edit it. D’oh!

Here is my site Read-Only: LINK
(how to share your site Read-Only link)