So, I was working on a project, I noticed that the figures are after where I want to place, So how to force an image to be one page before the already placed figure.In this case I want to swap the pages here. Adding picture for reference, I know it's a bit blur but you can get the idea. Figures are just for a reference. 
\begin{figure}[T]
\centering
\begin{subfigure}[b]{0.45\textwidth}
\centering
\includegraphics[width=\textwidth]{pic1.png}
\caption{Original }
\end{subfigure}
\begin{subfigure}[b]{0.45\textwidth}
\centering
\includegraphics[width=\textwidth]{pic2}
\caption{Original }
\end{subfigure}
\begin{subfigure}[b]{0.45\textwidth}
\centering
\includegraphics[width=\textwidth]{pc3}
\caption{Original }
\end{subfigure}
\begin{subfigure}[b]{0.45\textwidth}
\centering
\includegraphics[width=\textwidth]{pic4}
\caption{Encrypted }
\end{subfigure}
\begin{subfigure}[b]{0.45\textwidth}
\centering
\includegraphics[width=\textwidth]{pic5}
\caption{Encrypted }
\end{subfigure}
\begin{subfigure}[b]{0.45\textwidth}
\centering
\includegraphics[width=\textwidth]{pic6}
\caption{Encrypted }
\end{subfigure}
\caption{Caption.}
\end{figure}
Tis not a vaild placement forfigure. I'd suggest you read an introduction to LaTeX's floating mechanism. That being said, it is usually considered bad practice to put figures on pages before they were first referenced in text (that's what LaTeX's\label-\ref-mechanism is for). You might be interested in this here as well: https://tex.stackexchange.com/questions/2275/keeping-tables-figures-close-to-where-they-are-mentioned – Skillmon May 29 '23 at 17:57