1. Open the fitness application, then open the menu and select the fitness goal.

2. Choose the fitness goal you want to achieve, such as "exercise", "calories" or "distance".

3. Under the fitness goal you choose, you can use the number knob or the finger slider to select your goal.

4. After setting the fitness goal, you can choose the daily training time and schedule, and then click "Apply".

5. Continue to scroll down and you will see the "Fitness Record" section. You can check your progress there, including exercise type, duration, distance, calories and other statistics.

6. You can also open the activity application, which will automatically track all your walking activities and set goals according to your daily steps. After being set in the fitness goal, you can track your progress and be notified when the goal is completed.

These are the steps to set the fitness goal of the Apple Watch S8. You can set it according to the above steps and customize it according to your own needs and fitness goals. If you have other questions or need more detailed guidance, please refer to the official description of Apple Watch or consult Apple Customer Service.