Create a plan for your announcement. You’ll want to use your website, social media, and concerts to let know people that you have a winner (selected composer) and runner up.
On your website, a straightforward blog post on your home will be a good start, and then share this to your social media channels. If you want to create more excitement around your announcement, look at the example of ICCCJ where they announce the results on a live YouTube video (or pre recorded more recently). This would allow your community to interact with your organization and bring a more human touch to your opportunity.
When announcing this in concerts, tell your audience how the process was and how excited you are about this upcoming collaboration with the selected composer(s). Use your programs to include this news and thank your community for helping you supporting living composers. Let them know that they are part of this event as much as you can. The truth is that they are a big reason why you are making all of these effort!