To turn off the automatic motion detection function on Samsung Watch, you can follow the following steps (the following steps are based on Samsung Galaxy Watch Active 2, and there may be some differences between different models):

1. On the watch home screen, swipe down to open the shortcut panel.

2. In the shortcut panel, find and click the "Settings" icon, usually a gear-shaped icon.

3. In the setting menu, slide up or down to find the "Exercise and Fitness" option. Click to enter this option.

4. In the "Exercise and Fitness" menu, find the "Automatically detect exercise" option. Click to enter this option.

5. In the option of "Automatically detect motion", you can see various types of motion detection, such as walking, running, cycling and so on. Find the type of exercise you want to turn off, and then click it.

6. In the setting page of sports type, find and click "Close" or similar option to disable the automatic detection of this sports type.

Please note that the above steps may not be fully applicable to all Samsung watch models and operating system versions. If you encounter difficulties or can't find relevant options during operation, please refer to the user manual of the watch or contact Samsung customer service for further assistance.