Ask to define a username in LibreOffice's writer General page

How can i make a username appear in the fields “Created” and “Modified” in the General tab in LIbreOffice’s writer

There are several General subcategories in Tools>Options but none has Created not Modified attributes. And there is no General tab in Insert>Filed>More Fields.

Please edit your question to improve it. Don’t forget to mention OS name and LO version.

Created and Modified type fields are located in the DocInformation tab. When you select Author attribute, the field value is what you entered in Tools>Options, LibreOffice>User Data. But the field is non empty only after the first save (Created) or an additional save (Modified).

User Data