How to write multiple lines inside a box of flowchart made using TikZ?

documentclass{article}
usepackage{tikz}
usepackage{listings}
%usetikzlibrary{calc,positioning,angles,arrows.meta,quotes,intersections}
%usetikzlibrary{through}

begin{document}



   lstset{
    basicstyle=footnotesizettfamily,
    columns=flexible,
    frame=single,
    framerule=0pt,%
    backgroundcolor=color{gray!20},%
    xleftmargin=fboxsep,%
    xrightmargin=fboxsep,
    language=[LaTeX]TeX,%
    keywordstyle=color{blue},%
    texcsstyle=*color{red}bfseries,%
    texcs={end,begin,documentclass,graphicspath},%
    mathescape=false,escapechar=|,%
    literate={<B>}{textcolor{blue}{stringusepackage}}1
    {{ }{textcolor{red}{{}}1
    {}}{textcolor{red}{}}}1
    {[}{textcolor{green}{[}}1     
    {]}{textcolor{green}{]}}1     
}
    Taken straight from the pgf manual chapter 17.4.3 Text Parameters: Alignment and 
 Width for Multi-Line Text

textbf{Option1}--  you can use a {tabular} inside a node


begin{lstlisting}
tikz node [draw] {
    begin{tabular}{cc}
        upper left & upper right
        lower left & lower right
    end{tabular}
};end{lstlisting}tikz node [draw] {
    begin{tabular}{cc}
        upper left & upper right
        lower left & lower right
    end{tabular}
};
hfillbreak
textbf{Option2}-- use verb|| inside your node to mark the end of lines. This will 
only be done, however, if the align option has been given
begin{lstlisting}
    tikz[align=left] node[draw] {This is analign=left demonstration.};
end{lstlisting}tikz[align=left] node[draw] {This is analign=left demonstration.};
hfillbreak
begin{lstlisting}
    tikz[align=center] node[draw] {This is analign=center demonstration.};
end{lstlisting}
tikz[align=center] node[draw] {This is aalign =center demonstration.};
hfillbreak
The verb|| command takes an optional extra space as an argument in square brackets.
begin{lstlisting}
    tikz node[fill=yellow!80!black,align=right]
    {This is a[-2pt] demonstration text for[1ex] alignments.};
end{lstlisting}
tikz node[fill=yellow!80!black,align=right]
{This is a[-2pt] demonstration text for[1ex] alignments.};
hfillbreak
textbf{Option3}
begin{lstlisting}
    /tikz/text width=dimension
end{lstlisting}
This option will put the text of a node in a box of the given width (something akin to 
a {minipage}
of this width). If the node text is not as wide as dimension, it will
nevertheless be put in a box of this width. If it is larger, line breaking will be 
done.
begin{lstlisting}
tikz draw (0,0) node[fill=yellow!80!black,text width=3cm]
{This is a demonstration text for showing how line breaking works.};
end{lstlisting}
tikz draw (0,0) node[fill=yellow!80!black,text width=3cm]
{This is a demonstration text for showing how line breaking works.};
end{document}