Before pressing Tap to Connect, you need to make sure you go to the TomTom watch's Settings -> Phone -> Pair New. The TomTom watch will then become visible to the App. After you select the TomTom watch, you need to enter the PIN that you see on the watch. If there is any tracking data stored on the watch, it will get automatically downloaded to the App and then uploaded to TomTom's cloud servers.
For hardcore sports enthusiasts who own the OPPO R9s, the TomTom Multi-Sport Watch is a good companion which allows you to track your location, speed, and performance from the convenience of your phone.