You need to experiment with the other available applications. At your top level forum, select OPTIONS > EDITOR > CHANGE APPLICATION TYPE.
For example...
Forum:
Displays a list of sub-forums above a list of topics in the forum
Mixed:
Displays headings for any sub-forum and the topics within that sub-forum under each heading
Board:
Displays headings for any sub-forum above headings for topics. Sub-forums are displayed with with their description. Topics are displayed with quotes from replies
If you then choose something other than "Forum" as the application type for a sub-forum the possibilities expand...
It will be easier to help you if you post the URL of the forum you are trying to replicate. It should be possible to work out which application to use for the forum and sub-forums.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.