Following up on a postdoc application at an academic conference in person
You could try to reach out by email and tell them that you've applied for a postdoc position in their lab, and that you are going to be at the conference where you'd love a chance to discuss your research contributions and qualifications as well as the opportunities that they may have. If they have an interest and tell you as much, by the time you two meet you both know why you're talking to each other.