\againframe
is your friend. You need to provide a label to the first frame to be able to recall it later. And an overlay specification to tell beamer
, which slides should be shown before going to the next frame.
Here I used overlay specifications for the items, because this makes it easier to see, which item is shown on which slide.
\documentclass{beamer}
\setbeamercovered{transparent=25}
\begin{document}
\begin{frame}<1-2>[label=list]{List}
\begin{itemize}
\item<1-> Point A
\item<2-> Point B
\item<3-> Point C
\end{itemize}
\end{frame}
\begin{frame}{Explaning Point B}
Stuff on point B
\end{frame}
\againframe<3>{list}
\end{document}
Edit: without \againframe
you can only repeat the first frame. There just remove all overlay specifications. And the label for the first frame is no longer necessary.
\documentclass{beamer}
\setbeamercovered{transparent=25}
\begin{document}
\begin{frame}<1-2>{List}
\begin{itemize}
\item<1-> Point A
\item<2-> Point B
\item<3-> Point C
\end{itemize}
\end{frame}
\begin{frame}{Explaning Point B}
Stuff on point B
\end{frame}
\begin{frame}{List}
\begin{itemize}
\item Point A
\item Point B
\item Point C
\end{itemize}
\end{frame}
\end{document}