First, you have to create a dedicated page for each default page (Forums, Groups, Activities, Feeds, etc.). You can also just create a blank page and set a title on them to easily find them. 

To set the default pages:

    1. Navigate to the BuddyBoss dashboard - Pages.

    2. Under Component Pages, find and assign each default pages that you have created. You may refer to the image below:

    3. Don't forget to click on "Save Settings" below the page.