You can change the default HelpDesk homepage:
You can add any number of Modern Pages to your HelpDesk site. The pages you add will appear in the Site Pages library. If you want to set on of these as a homepage, please click on the Settings icon:
Then navigate to the Site Pages library (Site contents -> Site Pages). In the library, choose the page you’d like to make the homepage and click on the vertical ellipses (…) to the right of the page name. Choose Make Homepage: