When you start a dialog to open or save a document, LibreOffice initially displays your working directory. To change this directory:
Choose - LibreOffice - Paths.
Click My Documents and click the Edit button, or double-click on My Documents.
In the Select Path dialog, choose the working directory you want and click Select.
You also use this procedure to change the directory displayed by LibreOffice when you want to insert a graphic. Choose - LibreOffice - Paths - Images, then follow step 3.