You need to create a sandbox, add the custom dashboard to the page and publish the sandbox

Create a publishable sandbox (in a test-environment first!):

You only need to choose "Page Composer":

Then you click "Create and Enter" and navigate to the page that you want to edit:

Then you can add the content of your choice and edit the appearance etc on the different menus connected to the object:

When you are satisfied, you publish the sandbox and you are done 😉