If you want to use a custom domain name like app.my-blog.com for your application, the next step would be to CNAME that sub-domain to apps1.webcrumbz.net. This is done from the administrative interface (DNS Zones) of your domain name, provided by your hosting company. Please notice that each hosting service has slightly different ways to edit the above settings. If you need more help on the matter, you can either fire a support ticket with your hosting company or we can try to help you as much as possible once you’re telling us who’s your hosting provider.
If the CNAME is set up corectly, please note that it will take up to 12 hours for the DNS to propagate. In the meantime, the app.my-blog.com domain might not be accessible.