I cant really help without more information, but what i think you need to do is publish the game normally to your account, go to the jam page, click submit, choose an existing game (your game) and the rest is simple. hope this helps!

Dashboard > Create new project > Upload files (upload your game) > Save & view page > Edit game > Visibility & access (set to 'Public — Anyone can view the page'). After that, your project will appear as an option for submission in the jam's page.