You have one of two things in your document, for which you still didn't provide any sample (which you could get by simply removing all text): a table with two columns, or (more probable) two-column layout. The former might be removed by selecting TableDeleteTable (with cursor inside the table), while the latter is either a section formatting or a page style formatting. Sections can be managed in FormatSections, where you can simply delete sections (which will still keep the contents, only remove the section), and pages may be formatted using FormatPage. or in Page Styles sidebar.