Hello! We're very happy to hear that! :]
If you purchased the game here, go to your itch library, check the download page, and at the bottom there should be a "Generate Steam Key" button.
Is there a secondary method? I have been looking all over the page and cannot find the "Generate Steam Key" option. When I originally purchased the game I had an issue with the itch app not letting me download and had to download it through the itch website, so maybe that's why?