I found Nils Ahner at the site of Dieter Staedeli. Nils Ahner started in 2000 working with Ulrich Fries, Thonet Antik, in Berlin and started in 2016 his own Thonet and other bentwood furniture repair and trade shop in Berlin with the apt name Biegen oder Brechen (Bend or Crack). You can find the shop at the Bleibtreustrasse 53 in D-10623 Berlin, Germany.
Thank you