Cannot enable insert on text flow

Hello,
I have a document that a client would like for page 6 to start at page 1. However, when I try to enable insert on text flow, as described here: Page Numbers - LibreOffice Help
I am not allowed to.
Please help,
LF

Hello Lilia F,
if you want the first page of your document to have page number 6, then place your caret (cursor) in the very first text of your document, then choose Format - Paragraph - Text flow, and type the number 6 into the Page Number field.