This process is simple! Follow these steps and you will have a new Topic as a home page (default Topic) .
If you would like to set one of your Topics as your new home page, go to your Organization Dashboard.
From there, click on [Topics] on the left sidebar. Within the "All" team find the Topic you wish to set as the home page. Do not click into the Topic. There is a yellow outlined star at the top left corner of the Topic. Click on the star, make sure the star is filled in solid yellow and your new home page is set!
To unset the Home page Topic, click the star again.