\documentclass[12pt]{report}
\usepackage{float}
\usepackage{xepersian}
\renewcommand\bibname{مراجع}
\settextfont[Scale=1.1]{XB Zar}
\setlatintextfont[Scale=1.1]{Times New Roman}
\setdigitfont[Scale=1.1]{ParsiDigits}
\flushbottom
% ------------------------------------
\makeatletter
\renewcommand*\l@chapter[2]{%
  \ifnum \c@tocdepth >\m@ne
    \addpenalty{-\@highpenalty}%
    \vskip 1.0em \@plus\p@
    \setlength\@tempdima{1.5em}%
    \begingroup
      \parindent \z@ \if@RTL\leftskip\else\rightskip\fi \@pnumwidth
      \parfillskip -\@pnumwidth
      \leavevmode \bfseries
      \advance\if@RTL\rightskip\else\leftskip\fi\@tempdima
      \hskip -\if@RTL\rightskip\else\leftskip\fi
      #1\nobreak\leaders\hbox{$\m@th
        \mkern \@dotsep mu\hbox{.}\mkern \@dotsep
        mu$}\hfill \nobreak\hb@xt@\@pnumwidth{\hss #2}\par
      \penalty\@highpenalty
    \endgroup
  \fi}
\renewcommand\tableofcontents{%
    \if@twocolumn
      \@restonecoltrue\onecolumn
    \else
      \@restonecolfalse
    \fi
    \centerline{\huge\bfseries\contentsname
        \@mkboth{%
           \MakeUppercase\contentsname}{\MakeUppercase\contentsname}}%
    \vskip 40\p@
    \@starttoc{toc}%
    \if@restonecol\twocolumn\fi
    }
    
    \renewcommand{\@starttoc}[1]{%
  \hboxR to \textwidth{عنوان \hfill صفحه} 
  \begingroup
    \makeatletter
    \@input{\jobname.#1}%
    \if@filesw
      \expandafter\newwrite\csname tf@#1\endcsname
      \immediate\openout \csname tf@#1\endcsname \jobname.#1\relax
    \fi
    \@nobreakfalse
  \endgroup}
  
\makeatother

\titleformat{\chapter}[display]
  {\normalfont\LARGE\bfseries\centering}{}{20pt}{\LARGE}
\titlespacing{\chapter}{2pc}{4cm}{1cm}[2pc]

\begin{document}
\tableofcontents
\include{chap1}
\appendix
‎\makeatletter‎
\renewcommand\thechapter{\@arabic\c@chapter}
\makeatother‎
\baselineskip 27pt
\input{ap1}
\include{app1}
\end{document}