A simple but sufficient setup to response to a review. The rev command guards that response is given and prints a red note otherwise.

main.png

main.tex:

\documentclass[a4paper,USenglish]{article}
\usepackage{xcolor}
\newcommand{\rev}[2]{ \item #1 \if\relax\detokenize{#2}\relax {\color{red}UNANSWERED} \else {\color{blue}#2} \fi }
\begin{document}
\section*{Response}
We thank the reviewers for their reviews \dots

\subsection*{Reviewer 1}
\begin{enumerate}
    \rev{Line 128: \dots}{}
    \rev{Line 256: \dots}{we changed this}
\end{enumerate}

\end{document}