Help Required - regarding Arrows in flowchart

Here's one way to do it with just nodes and arrows manually setting the sizes of all boxes.

documentclass[tikz, border=20]{standalone}
usetikzlibrary{calc}
begin{document}
    begin{tikzpicture}
        node[minimum width=4cm, minimum height=2cm, draw] (A) at (0, 0) {};
        node[minimum width=4cm, minimum height=1cm, draw] (B) at ($(A) + (0, -3)$) {};
        % Note 1.41 ~= sqrt(2)
        node[minimum width=1.41*2cm, minimum height=1.41*2cm, rotate=45, draw] (C) at ($(B) + (0, -4)$) {};
        draw[->] ($(A.north) + (0, 1)$) -- (A.north);
        draw[->] (A.south) -- (B.north);
        draw[->] (B.south) -- (C.north east);
        draw[->] (C.south west) -- ($(C.south west) + (0, -1)$);
        coordinate (D) at (-3, 0);
        draw[->] (C.north west) -- (C.north west -| D) -- (A.west -| D) -- (A.west);
    end{tikzpicture}
end{document}