Welcome to the forum.
You don't say whether you are generating the help from the
menu, the icon, or under Single Source Layouts in Project Manager
(where you see your topics listed).
Go to Single Source Layouts and double click the HTML help
option. You will see the default topic is listed there. You can
change it to whichever of your topics you want.
Help others by clicking Correct Answer if the question is answered. Found the answer elsewhere? Share it here. "Upvote" is for useful posts.