Put text at a heading given the page number

Question

Following up, my question is now to replace the text of the heading with a dummy text. I tried multiple options at Line 16, but the text does not seem to go above the margin. Assuming this is solvable, the problem still remains as how to find the exact location for the header text.

% Shamelessly copied from https://www.overleaf.com/learn/latex/Headers_and_footers
\documentclass{article}
\usepackage[english]{babel}
\usepackage[utf8]{inputenc}
\usepackage{fancyhdr}
\usepackage{lipsum}


% https://tex.stackexchange.com/a/572688/38244
%%%%%%%%% How to get the heading location?
\usepackage{eso-pic}
\AddToShipoutPictureFG{% Place something in the page ForeGround...
    \AtTextUpperLeft{% ...at the text block upper left corner...
        \ifnum\value{page}=3 % ...only on page 3...
        \makebox[\textwidth]{% ...in the horizontal centre of the text block...
            \raisebox{\dimexpr-.5\height-.5\textheight}{% ...at the vertical centre of the text block
                \Huge RaNDoM TeXT 
            }%
        }%
        \fi
    }%
}

\pagestyle{fancy}
\fancyhf{}
\rhead{Overleaf}
\lhead{Guides and tutorials}
\rfoot{Page \thepage}

\begin{document}
    
    \section{First Section}
    
    Hello,  here  is  some  text  without  a  meaning.   This  
    text  should  show  what  a printed text will look like at 
    this place.  If you read this text, you will get no information.  
    Really?  Is there no information?  Is there a difference between 
    this ...
    
    \lipsum[1-50]
    
    %%%%%%%%%%% Write something on the header of page 3 to replace the current heading
\end{document}

Answer 1

There is no need for using eso-pic if you only want to place content in the headers conditionally. For that, just place your condition directly inside the header/footer:

\documentclass{article}

\usepackage{fancyhdr}
\usepackage{lipsum}

\pagestyle{fancy}
\fancyhf{}
\rhead{\ifnum\value{page}=3 Not Overleaf\else Overleaf\fi}
\lhead{\ifnum\value{page}=3 Something else\else Guides and tutorials\fi}
\rfoot{Page \thepage}

\begin{document}

\section{First section}
\sloppy\lipsum[1-50]

\end{document}