One thing that someone recently said in a talk is that Imposter Syndrome is experienced by senior developers who do not feel adequately prepared or trained for their current position, as opposed to new developers who don't feel ready. Maybe this will be an interesting point of discussion for your talk.
In my case, I'm a career switcher as well (French Ph.D in 1998., experienced a terrible academic job market, and then caught the internet at a great time to self-train and move up). 15 years later I am quite sure I'm not the greatest developer in the history of development. I do believe, however, that I bring something else to the table, which is a diverse perspective and a willingness to learn. If you can find it within yourself to value your own perspective as something that few others might have, and share it in a spirit of helpfulness, that is a powerful gift to give. And then if you can also take your accumulated skills and experience and use them to teach others, that is a great way to rid yourself of imposter baggage. So for me, the key is - value your experience and uniqueness, and make sure to pass on your knowledge.