Berlin is a city of long distances but with good public transport systems. Access to a suitable station is thus much more important than pure geographical distance.
The tournament venue "Japanisch-Deutsches Zentrum Berlin" is located in Berlin Dahlem, a quiet quarter in the south-west of Berlin. If you plan to spend the nights in the party quarters of downtown, one option is to find an accommodation along the subway line U3 (see below). If you do not mind changing the subway, a more centrally located accommodation is no problem.
Anyway, you will find many accommodations for just about any budget on the well-known booking platforms.
Clayallee 150-152, 14195 Berlin
Distance 400 m
Price 79,- Euro
Unter den Eichen 89A, 12205 Berlin
Distance 1,6 km
Price 55,- Euro
If you do not want to change trains, which would not be a problem, stay near the U3 subway line. Cheap hostels are located especially near the stations "Augsburger Straße" and "Spichernstraße" as well as "Heidelberger Platz". The travel time to "Oskar-Helene-Heim" from these stations is about 15 minutes.