For importing SVG drawings, it is better to use the svg package than to manually \input them. (See this answer for details on how to set it up.) This package does not provide a trim option, but the adjustbox package lets you trim (and clip) anything just like with \includegraphics.
So, after loading the packages
\usepackage[inkscapearea=page]{svg}
\usepackage{adjustbox}
you can trim your drawing
\adjustbox{trim=1cm 2cm 3cm 4cm}{%
\includesvg{MessAbsch}%
}
Note that \includegraphics always trims first and scales after, but with adjustbox you will trim last. Thus, if you want your final drawing to have a width of 6cm, you will have to include it too large before trimming.
\adjustbox{trim=1cm 2cm 3cm 4cm}{%
\includesvg[width=9cm]{MessAbsch}%
}
This approach also works with \input, of course, but using svg comes with several advantages that make using it worthwhile.