How to input an arrow before a node in Tikz

Im currently using Tikz to cite a mathematical model from a research but I don't know how to input an arrow before the node.

Here's a photo of the mathematical model that I'm trying to code:

I don't know how to input the arrow entering the node F with dr above. Currently, this is all i have

\tikzstyle{Box} = [rectangle, rounded corners, 
minimum width=1.25cm, 
minimum height=1.25cm,
text centered, 
draw=black, fill=yellow!30]

\tikzstyle{arrow} = [thick,->,>=stealth]

\begin{center}
    \begin{figure}
        \centering
    \begin{tikzpicture}[node distance=2cm]
        \node (F) [Box,  label=above:{\textcolor{red}{$I_1$}}] {$F$};
        \ 
        \node (D) [Box, right of =S, label=above:{\textcolor{red}{$I_2$}}] {$D$};
        \ 
        \node (W) [Box, right of =D, label=above:{\textcolor{red}{$I_3$}}] {$W$};
        \ 
        \node (R) [Box, right of =W, label=above:{\textcolor{red}{$I_4$}}] {$R$};

\draw [arrow] (F) -- node[above]{\textcolor{red}{$\varphi_1$}}(D);
\draw [arrow] (D) -- node[above]{\textcolor{red}{$\varphi_2$}}(W);
\draw [arrow] (W) -- node[above]{\textcolor{red}{$\varphi_3$}}(R);
        
    \end{tikzpicture}
    \end{figure}
\end{center}

I hope anyone can help me resolve this problem. Thank you so much.

You can add an empty node "left of" your first box and then draw the arrow just like you do for your other arrows:

\documentclass{beamer}

\usepackage{tikz}
\tikzset{
  Box/.style={
    rectangle, 
    rounded corners, 
    minimum width=1.25cm, 
    minimum height=1.25cm,
    text centered, 
    draw=black, 
    fill=yellow!30
  },
  arrow/.style={
    thick,
    ->,
    >=stealth
  }
}

\begin{document}
	
\begin{frame}

\begin{figure}
\begin{tikzpicture}[node distance=2cm]
  \node (F) [Box,  label=above:{\textcolor{red}{$I_1$}}] {$F$};
  \node (D) [Box, right of =F, label=above:{\textcolor{red}{$I_2$}}] {$D$};
  \node (W) [Box, right of =D, label=above:{\textcolor{red}{$I_3$}}] {$W$};
  \node (R) [Box, right of =W, label=above:{\textcolor{red}{$I_4$}}] {$R$};
  \node (foo) [left of=F] {};
  \draw [arrow] (F) -- node[above]{\textcolor{red}{$\varphi_1$}}(D);
  \draw [arrow] (D) -- node[above]{\textcolor{red}{$\varphi_2$}}(W);
  \draw [arrow] (W) -- node[above]{\textcolor{red}{$\varphi_3$}}(R);
  \draw [arrow] (foo) -- node[above]{\textcolor{red}{dr}}(F);        
\end{tikzpicture}
\end{figure}

\end{frame}	
	
\end{document}