You may need to define a new style, and then change style in the document. Either change it within a group or environment to keep the style change local, or change back to default afterwards.

\documentclass{article}
\usepackage{datetime2}
\DTMnewdatestyle{yyyymm}{%
\renewcommand\DTMdisplaydate[4]{##1/\DTMtwodigits{##2}}%
\renewcommand\DTMDisplaydate[4]{##1/\DTMtwodigits{##2}}%
}
\begin{document}
\DTMdate{2000-12-30} %Should be printed as: 2000/12
{% pair of braces makes the new style local
\DTMsetdatestyle{yyyymm}
\DTMdate{2000-12-30}
}
\DTMdate{2000-12-30}
\DTMsetdatestyle{yyyymm}
\DTMdate{2000-12-30}
% or you can set the style back to default
\DTMsetdatestyle{default}
\DTMdate{2000-12-30}
\end{document}
\documentclass{...}, the required\usepackage's,\begin{document}, and\end{document}. That may seem tedious to you, but think of the extra work it represents for TeX.SX users willing to give you a hand. Help them help you: remove that one hurdle between you and a solution to your problem. – Stefan Pinnow Mar 22 '18 at 08:59\datedoes not have an optional argument, neither by standard LaTeX nor by thedatetimeadditions. – Mar 22 '18 at 10:24\dateon its own doesn't actually typeset anything. It only sets what should be displayed by\maketitle. – Torbjørn T. Mar 22 '18 at 13:30