After you have opened the App, go to the watch's settings and select Phone -> Pair New. Tap on the App to start searching for the watch.
Once the App has found the TomTom, select the TomTom Watch. You'll then need to enter the PIN code displayed on the watch into the App.
Once pairing is successful, your watch will show Connected.
You can start using the App to track your location, speed, etc. from the convenience of your phone.