Registration at the City
...If you are an EU citizen, please contact the Bürgerdienste(Opens in a new tab) in the city center as soon as possible after your arrival in Dortmund.
...If you are a non-EU citizen, please contact the Bürgerdienste International(Opens in a new tab) , also known as "Ausländerbehörde der Stadt Dortmund", as soon as possible after your arrival in Dortmund.
You do not live in Dortmund, but in antoher city (e.g. Bochum, Essen, Witten, etc.)? In this case, you have to register there and not in Dortmund.