If you didn't set your app's domain when you created it in ServerPilot (or if you need to change it), don't fret. ServerPilot makes it easy to add a domain to your app or to remove a domain you no longer use.
First, open your app in ServerPilot by selecting it from the list on the Apps screen.
Under your app's Domains tab, enter any domains or subdomains for the app both with and without the www., clicking Add after each one.
Be sure to add all of the domains that can be used to reach your app, even if you don't want the domain to be displayed in the URL. If you do not want one of your app's domains displayed, you can redirect it to the domain you do want shown; for example, redirecting www to non-www.
If you need to remove a domain form your app, simply hover over the domain and click the red X to the left.
Don't forget to set your DNS with both your server provider and registrar.