Well, you can do this by your own with a little bit try and error like this:
- Copy the definition of command
\cventry into your other class in the preamble and use command \cventry in the document.
- Compile and see the resulting error:
command \cvitem is undefined.
- Copy the definition of command
\cvitem into the preamble. Do not forget to add the needed packages (calc, xcolor and ifthen) ...
- Compile and see the resulting errors: some more definitions are missing.
- Copy the missing definitions into the preamble and compile again.
- If you got all missing definitions the code can compile now.
Please see the following example for class article and command \cventry:
\documentclass{article}
\usepackage{calc} % <=================================================
\usepackage{xcolor} % <=================================================
\usepackage{ifthen} % <=================================================
% <================== added code from moderncv.cls and moderncvbodyi.sty
\newcommand*{\cventry}[7][.25em]{%
\cvitem[#1]{#2}{%
{\bfseries#3}%
\ifthenelse{\equal{#4}{}}{}{, {\slshape#4}}%
\ifthenelse{\equal{#5}{}}{}{, #5}%
\ifthenelse{\equal{#6}{}}{}{, #6}%
.\strut%
\ifx&%
\else{\newline{}\begin{minipage}[t]{\linewidth}\small#7\end{minipage}}\fi}}
\newcommand*{\cvitem}[3][.25em]{%
\begin{tabular}{@{}p{\hintscolumnwidth}@{\hspace{\separatorcolumnwidth}}p{\maincolumnwidth}@{}}%
\raggedleft\hintstyle{#2} &{#3}%
\end{tabular}%
\par\addvspace{#1}}
\newlength{\hintscolumnwidth}
\setlength{\hintscolumnwidth}{0.175\textwidth}
\newlength{\separatorcolumnwidth}
\setlength{\separatorcolumnwidth}{0.025\textwidth}
\newlength{\maincolumnwidth}
\setlength{\maincolumnwidth}{\textwidth-\leftskip-\rightskip-\separatorcolumnwidth-\hintscolumnwidth}
\definecolor{color0}{rgb}{0,0,100} % <================================== blue
\newcommand*{\hintfont}{\mdseries} % <================================== bold
\newcommand*{\hintstyle}[1]{{\hintfont\textcolor{color0}{#1}}}
\begin{document}
\section{Test}
This is a usual paragraph in the document. This is a usual paragraph in the document.
This is a usual paragraph in the document. This is a usual paragraph in the document.
This is a usual paragraph in the document. This is a usual paragraph in the document.
\section{Education}
\cventry{year--year}{Degree}{really very long Institution--3}{very long City--4}{\textit{Grade}--5}%
{This is a very long description--6. This is a very long description.
This is a very long description. This is a very long description.
This is a very long description. This is a very long description}
\end{document}
and see its resulting pdf page:

\cventry? What is with the\sectioncommand etc.? – Mensch Feb 13 '20 at 10:00koma-moderncvclassic(search for it on CTAN) that is already done. For a simple example please have a look to this question: https://tex.stackexchange.com/q/466746/16550 – Mensch Feb 13 '20 at 22:45\sectionis changed too? Why do you not simply usepdfpagesto include your cv into the other document? – Mensch Feb 14 '20 at 10:07