How can I divide my thesis into two volumes with each volume containing three chapters?

My code is:

documentclass[11pt,a4paper,oldfontcommands, twoside]{memoir}
usepackage[utf8]{inputenc}
usepackage[inner=4cm,outer=2cm]{geometry}
usepackage{lmodern, parskip}
usepackage[compact]{titlesec}
usepackage{amssymb,amsmath,amsfonts}
setlength{parskip}{5pt}
usepackage{mathrsfs}
usepackage{bm}
usepackage[noadjust]{cite}
usepackage{mathtools}
usepackage{float}
usepackage{bbm,enumitem}
setenumerate[1]{label={(roman*)}} % Global setting
usepackage{soul,calc,xcolor,a4wide}
usepackage{centernot,graphicx,algorithmic}
usepackage[chapter]{algorithm}
usepackage{setspace}
usepackage[pdfpagelabels,linktocpage=true,colorlinks=false]{hyperref}
makeatletter
letHy@linktocHy@linktoc@none
makeatother
hypersetup
{
    pdfauthor={.....},
    pdfsubject={},
    pdftitle={},
    pdfkeywords={},
   }

usepackage{amsthm}
usepackage{url}
usepackage{bookmark}
usepackage{memhfixc}
renewcommand{baselinestretch}{1.15}
definecolor{nicered}{rgb}{.0588,.0941,.333}
setsecheadstyle{color{nicered}Largebfseriessffamilyraggedright}
setsubsecheadstyle{largesffamilyraggedright}
setsubsubsecheadstyle{normalsizesffamilyraggedright}

setlist[enumerate]{noitemsep, topsep=0pt}

%%%FORMATING FOR CHAPTER
makeatletter
newlengthdlf@normtxtw
setlengthdlf@normtxtw{textwidth}
defmyhelvetfont{defsfdefault{mdput}}
newsavebox{feline@chapter}
newcommandfeline@chapter@marker[1][4cm]{%
sboxfeline@chapter{%
resizebox{!}{#1}{fboxsep=1pt%
colorbox{nicered}{color{white}bfseriessffamilythechapter}%
}}%
rotatebox{90}{%
resizebox{%
heightof{usebox{feline@chapter}}+depthof{usebox{feline@chapter}}}%
{!}{scshapeso@chapapp}}quad%
raisebox{depthof{usebox{feline@chapter}}}{usebox{feline@chapter}}%
}
newcommandfeline@chm[1][4cm]{%
sboxfeline@chapter{feline@chapter@marker[#1]}%
makebox[0pt][l]{% aka rlap
makebox[1cm][r]{useboxfeline@chapter}%
}}
makechapterstyle{daleif1}{
renewcommandchapnamefont{normalfontLargescshaperaggedleftso}
renewcommandchaptitlefont{normalfontLargebfseriescolor{nicered}}
renewcommandchapternamenum{}
renewcommandprintchaptername{}
renewcommandprintchapternum{nullhfillfeline@chm[2cm]par}
renewcommandafterchapternum{parvskipmidchapskip}
renewcommandprintchaptertitle[1]{chaptitlefontraggedleft ##1par}
}
renewcommand{secheadstyle}{large bfseries color{nicered} 
memRTLraggedright}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
newcommand{rmnum}[1]{romannumeral #1}
newcommand{Rmnum}[1]{expandafter@slowromancapromannumeral #1@}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
makeatother
chapterstyle{daleif1}
setcounter{secnumdepth}{3}
allowdisplaybreaks

captionnamefont{smallsffamilybfseries}
captiontitlefont{smallsffamily}

makepagestyle{myruled}
makeheadrule {myruled}{textwidth}{2pt}
makefootrule {myruled}{textwidth}{2pt}{footruleskip}
makeevenhead {myruled}{}{smallsffamilyleftmark}{}
makeoddhead {myruled}{}{smallsffamilyrightmark}{}
makeevenfoot {myruled}{smallthepage}{}{}
makeoddfoot {myruled}{}{}{smallthepage}

setlength{oddsidemargin}{6mm}
setlength{evensidemargin}{-6.9mm}

makeatletter % because of @chapapp
makepsmarks{myruled}{
  nouppercaseheadscreatemark{chapter}{both}{shownumber}{
  @chapapp }{. }
  createmark{section}{right}{shownumber}{}{.  }
  createmark{subsection}{right}{shownumber}{}{.  }
  createmark{subsubsection}{right}{shownumber}{}{.  }
  createplainmark {toc}{both} {contentsname}
  createplainmark {lof}{both} {listfigurename}
  createplainmark {lot}{both} {listtablename}
  createplainmark {bib}{both} {bibname}
  createplainmark {index}{both} {indexname}
  createplainmark {glossary}{both} {glossaryname}
}
makeatother

newcommand{mar}[1]{marginpar{small it #1}}
marginparwidth 1 in

%renewcommandqed{$blacksquare$}



begin{document}
%% Some pages before contents
pagenumbering{gobble}
include{cover}
cleardoublepage
include{declaration}
cleardoublepage
include{acknowledgement}
cleardoublepage
include{dedication}
cleardoublepage
pagenumbering{roman}
cleardoublepage
setcounter{tocdepth}{2}
begingroup
setlength{beforechapskip}{0.0 pt}
pdfbookmark[0]{Contents}{toc}
tableofcontents*
endgroup
cleardoublepage
pagenumbering{arabic}
pagestyle{myruled}
% Here I want to add "Volume 1"
include{Ch1}
include{Ch2}
include{Ch3}
% Here I want to add "Volume 2"
include{Ch4}
include{Ch5}
include{Ch6}

end{document}