Hi,
At first, you need to set the
Extension less URLs, so you will be able to access the page without extension (.aspx).
You may also need to set the
Trailing slash setting or to use it just for
extension less urls.
Then, underneath the node, you will create a document named "default". After this, select the parent document, go to the Properties tab -> Menu section and set the URL redirection field to redirect to the default document you have just created under this node.
Best regards,
Juraj Ondrus