>>512671074 (OP)
Cultivate a healthy friendship, see if it can become a romance and then there are so many ways of presenting working out as a goal you two do together. It may not even be that you start out doing so together in the same space, but there's a charm to wanting to becoming healthier for each other. I say this as someone who dated a girl who was concerned about her weight and other girls having better figures, but I wasn't peak fitness either so we both just started working out at home.
Alternatively, you can meet someone at the gym but then you're hoping you click with someone there despite the fact that you're both likely focusing on your workout with what little time you have to be there and do so. She'll expect that at minimum so you'll have to hint at your interests and lifestyles, perhaps you write, draw, compose, etc. during your breaks between reps. Perhaps someone you meet at the gym will take note of that. I've outright gone up to people to ask them out and that's how I had my first relationship, but that was after hours rather than in a place like the gym.