Look for a blue and white umbrella at Senate Square (or Senaatintori in Finnish). The guide also holds a blue sign that reads "Finntastic Walking Tour".
In these dates, 23.09 - 27.09 (international market) 27.11-22.12 (Christmas market) the guides will be standing right next to the big stairway
The tour ends at Oodi central library, next to the central train station, within 15 minutes walking distance from Senate square.