Edit / style plugin added content

I wasn’t really sure how to name this topic.

Sometimes a plugin adds content to a page. This can be for example woo products on the shop page, but also a product designer on a single page.
These pages, when you open them in the CMS, the content is blank.
Even with the plain source / text editor, you don’t see anything there.
This is a problem for me, because now I cannot change anything.
For example. I want to add some empty space above the content.
But everything I do in the editor, will be shown below the content on the page.
Can anyone tell me what to do?