Mittels
\renewcommand*{\partheadstartvskip}{%
\null\vskip20pt
}
\renewcommand*{\partheadendvskip}{%
\null\vskip-1pt
}
Hier ein minimales Skript:
\documentclass[a4paper]{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\usepackage{array}
\usepackage[bookmarks=true]{hyperref}
\usepackage{bookmark}
\usepackage{lipsum}
\title{title}
\renewcommand*{\partheadstartvskip}{%
\null\vskip20pt
}
\renewcommand*{\partheadendvskip}{%
\null\vskip-1pt
}
\begin{document}
\maketitle
\pdfbookmark[-1]{Front Matter}{frontmatter}
\pdfbookmark{\contentsname}{Contents}
\tableofcontents
\part{Ein Test}
\lipsum[1]
\chapter{P}
Some text
\end{document}