You can easily set a custom domain for your dedicated landing page in a few easy steps.
Click on the Promote tab from the top menu on your dashboard:
Then click on Landing Page from the left hand sidebar:
And then on the Options tab:
The custom domain you insert can be a domain you have previously purchased like: www.example.com
Before you insert that domain in the Custom Domain text box, make sure that the record cname of that domain on your server leads back to AppsBuilder, like this: cname.apps-builder.com