You arrive at the train station "Dortmund Hbf" or "Bochum Hbf", continue your journey with the S-Bahn transit S1and step off the S1 at the station "Dortmund Universität". The S1 drives every 20 min on weekday and it takes 6 min to reach the university from "Dortmund Hbf" or 20 min if you start at "Bochum Hbf".
You can determine your individual timetable on www.vrr.de.
For the way from the train station "Dortmund Universität" to the chair you can use the information given for walking.