The speech rate for workout guidance of the TrainAsONE mobile app is controlled from the Workout Settings screen.
The Workout Settings screen is accessible from the Settings screen via the main navigation drawer, and contains a section called Voice Options, one of which is a Rate slider to determine the rate of speech.
You can hear a sample of speech on the Workout Settings screen by pressing one of the 'bullhorns' to the right of either the 'Running Too Slow' or 'Running Too Fast' fields.