Glad to answer for you!
Please don't worry, just follow my footsteps.
1: Please turn on the Wi-Fi or traffic (3G, 4G) network in the iPhone first, and then turn on Bluetooth, so that the iPhone and Apple Watch can be connected and paired first.
2: Please open the (fitness activity) of Apple Watch first, then slide to the left and enter basic information such as height and gender. Then click (start using) on Apple Watch.
3. Another way is to enter basic information such as height and gender in the Apple Watch on the iPhone, and then press the lower left corner of the iPhone (my watch) and click (Health).
Furthermore, during the exercise, parents can change the fitness guide at will. Please open it on Apple Watch first, and then press and hold the screen of Apple Watch until the words (change the activity target) appear. Let go of your fingers. I wish you a happy life and every day.
All the original answers come from: 0k California 99.