You should remember your relationship. You are the consumer and he is the server. He has an obligation to help you when you encounter problems. For a simple example, you can ask him some questions about fitness, such as how to use this equipment and how to exercise at this stage. The coach in the gym will definitely answer your questions.
So that two people can start a good conversation. When two people are talking excitedly, you can say, "You are so professional, I can ask you for a contact information. Usually, I will ask you if I have any questions. " There is such a saying that he will definitely not refuse you.
Gym coaches are generally not short of admirers. Gym coaches are often in good shape, which can give girls a lot of security, and this alone can win the favor of many girls. So, when you choose to chat up, don't be coy. You can go up and talk to him directly and generously. Coaches are generally enthusiastic and especially good at communicating with people.