When you edit a section, you have all the same options as when you edit a page. The section that appears in edit mode will include everything below heading you selected Edit section, up until the next heading level that matches the level you selected.
If the Heading you wish to Section Edit is placed within a Conditional Content block, you must ensure that the Conditional Content block is not a direct child of a parent HTML element. Otherwise, the section will not have the option to Edit.