Coming from which airport? Tegel: than public transport is fine (20-30 minutes). Schonfeld: by bus and subway but better by taxi (depending on time 35-50 minutes), costs 45-50 €. For public transport you may download the app BVG FahrInfo. In case you're deciding to use public transport, consider the special offers.
Take the S-Bahn or airport express from the airport train station to Zoologischer Garten train station, it's then a 5 minute walk to the hotel. The ride takes around 30-40 minutes. There are lots of people on hand and willing to help at the airport information desk and train stations if you are unsure about anything I.e. Ticket machines, platforms, directions etc. People in Berlin are very friendly. Enjoy your trip.
Get an answer from Wyndham Berlin Excelsior staff and past guests.