\documentclass[a4paper,12pt]{report}
\usepackage{graphicx} % inserting images
\usepackage{graphics}
%\usepackage{hyperref} % PDF links
\usepackage{amsmath,amsthm,amssymb} %Liberary for math typing
\usepackage{setspace} % for switching between double/single space in document
\usepackage{fancyhdr} % package for changing Headings style
%دو خط زیر برای این هست که شماره بندی زیر نویسها را در هر صفحه جداگونه انجام دهد
\usepackage{perpage}
\MakePerPage{footnote}
% setting the margins of page
\usepackage[top=3cm,right=3cm,bottom=2.5cm,left=2.5cm]{geometry}         
\usepackage[pagebackref=true,colorlinks,linkcolor=blue,citecolor=magenta]{hyperref} %a pachage for colored refs and links        
\usepackage{xepersian}

% tell tex engine address of folder containing your pictures
\graphicspath{{images/}}
% commands to print the page number in header
\pagestyle{fancy}
\cfoot{}
\lhead{\thepage}

% commands related to XePersian package
\settextfont[Scale=1.1]{XB Yas}
\setdigitfont{XB Zar}
\setlatintextfont{LinLibertine}
% ------------------------------------- 




%برای چپ چین شدن عنوان فصل ها -----------------------------------------------------------------------------------------------------------------------------
\makeatletter
\def\@makechapterhead#1{%
  \vspace*{50\p@}%
  {\parindent \z@ \raggedright \normalfont
    \ifnum \c@secnumdepth >\m@ne
        \Large\bfseries \@chapapp\space \thechapter
        \par\nobreak
        \vskip 20\p@
    \fi
    \interlinepenalty\@M
    \Large \bfseries #1\par\nobreak
    \vskip 40\p@
  }}
\makeatother
%---------------------------------------------------------------------------





\begin{document}



%%%%%%%%%%%%%%%%%%%%%%%اینجا از این دستور برای تغییر اندازه فونت section  استفاده کرده ام%%%%%%%%%%

\setkomafont{section}{\large}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% insert each of your chapters with a \inlcude{filename} command as below
\doublespacing
%\include{chap1}

% -----------------------------------------------------------------------


\end{document}