documentclass[a4paper, 12pt]{article}
        usepackage{hyperref}
        usepackage{amsmath,amssymb,slashbox,graphicx}
    usepackage{float}
        begin{document}

begin{figure}[h]
    includegraphics[width=1textwidth,height=180px]{test1234}
    caption{test1234}label{test1234}
end{figure}

blabla ref{test1234}
       blabla ref{test123}

        section*{Appendix}

        setcounter{table}{0}
        renewcommand{thetable}{A.Tab.arabic{table}}
        setcounter{figure}{0}
        renewcommand{thefigure}{A.Abb.arabic{figure}}
        setcounter{figure}{0}

        begin{figure}[H]
            includegraphics[width=1.0textwidth]{test}
            caption{test}label{test123}
        end{figure}



        end{document}

documentclass[a4paper, 12pt]{article}
usepackage{hyperref}
usepackage{amsmath,amssymb,slashbox,graphicx}
usepackage{float}
begin{document}

begin{figure}[h]
  includegraphics[width=1textwidth,height=180px]{example-image-a}
  caption{test1234}label{test1234}
end{figure}

blabla ref{test1234}
blabla ref{test123}

section*{Appendix}

renewcommand{thetable}{A.Tab.arabic{table}}
renewcommand{thefigure}{A.Abb.arabic{figure}}
renewcommand{theHtable}{A.Tab.arabic{table}}%<---!!!!---
renewcommand{theHfigure}{A.Abb.arabic{figure}}%<---!!!!---
setcounter{table}{0}
setcounter{figure}{0}

begin{figure}[H]
  includegraphics[width=1.0textwidth]{example-image-b}
  caption{test}label{test123}
end{figure}

end{document}